How to Play a Harmonica
To play the harmonica, start by practicing blowing into 1 hole to make a note. If you want to bring each note up a step, breathe in through the harmonica. Once you've mastered this, try playing a C scale, which on a C-tuned diatonic harmonica begins with up-4 and moves up to up-7. To play each note, breathe out through each hole before breathing in, apart from on the 7th hole, where you breathe in first. When you reach the point of being able to play the C scale and single notes confidently, consider taking lessons to become a more advanced player.
Choose a harmonica. There are many different types of harmonica available for purchase, which vary in use and price. For now, purchase either a diatonic or a chromatic harmonica. Either type can be used to play most popular music, such as blues or folk. The diatonic harmonica is arguably the most common type available, and certainly the cheapest. It's tuned to a specific key, which can't be changed. Most diatonic harmonicas are tuned to the key of C. Types of diatonic harmonica include the “blues harmonica,” the “tremolo harmonica,” and the “octave harmonica.” In the western world, the blues harmonica is common; in east Asia, the tremolo harmonica is seen more often. The chromatic harmonica is a type of harmonica that uses a mechanical apparatus to control which holes make noise. Basic chromatic harmonicas with 10 notes can only play one full key (the same as a diatonic harmonica), but chromatics with 12-16 holes can be tuned to any key. Chromatics are considerably more expensive than most diatonic harmonicas; a quality chromatic from a reputable brand can cost several hundred dollars. Because of their flexibility, 12-plus-note chromatic harmonicas are generally preferred for jazz music. A common shorthand term for the harmonica is the “harp.” This comes from its other traditional names, including “French harp” and “blues harp.” As long as the context is clear, the words “harmonica” and “harp” can be used interchangeably. Learn about your harmonica. The harmonica is a reed instrument that uses brass reeds. The reeds are what split the air you push or pull through the holes to create tones. Reeds are mounted on a plate, sensibly called the reed plate , which is also usually made of brass. The part of the harmonica that the reed plate is mounted to is called the comb , and is typically made of plastic or metal. The mouthpiece of the harp may be integrated into the comb, or in chromatic harmonicas, screwed on separately. The cover plates cover the rest of the apparatus, and can be made of wood, metal, or plastic. A chromatic harp's sliding bar is also usually made of metal. Depending on whether you inhale or exhale through your harp, different notes are produced by the reeds. A typical diatonic harp tuned to C on the exhale is tuned to G on the inhale. These scales complement each other nicely, each filling in the other without having to add extra holes. The reeds inside your harmonica are delicate and will wear out over time. Gentle playing and regular care are required to maintain a good tone as long as possible. Learn to read harmonica tablature. Like guitars, harmonicas can be played by following tablature, which reduces the notes on a sheet of music down to an easy-to-follow system of holes and breath patterns. Tablature is useful for larger chromatic harmonicas as well, but it differs somewhat from diatonic tablature, and is less common. Breathing is marked by arrows. An up arrow indicates a breath out; a down arrow indicates a breath in. Most holes on a diatonic harmonica produce two “neighbor” notes on a given scale; thus playing C and then D on the same scale is accomplished by blowing into the appropriate hole, and then drawing in from the same hole. Holes are marked with a number, starting from the lowest (left-hand) tone and moving upward. Thus, the lowest two notes are (up) 1 and (down) 1. On a 10-hole harp, the highest note would be (down) 10. Some notes on a regular 10-hole harmonica overlap, notably (down) 2 and (up) 3. This is necessary to allow proper range for playing scales. More advanced techniques are marked with slashes or another small mark. Diagonal slashes through the arrows indicate that note bending (covered later) is required to get the proper tone. Chevrons or slashes on chromatic tablature can also indicate whether or not to hold the button in. There isn't a standardized system of tablature that's used by all harmonica players. However, once you practice and get comfortable reading one type, most other types will make sense to you quickly. Make a note by blowing. The very first thing to practice with your new instrument is making a note. Pick a hole or a set of holes on the mouthpiece and blow gently into them. Neighboring holes are typically designed to harmonize with each other automatically, so try blowing into three holes at once to make a pleasing sound. Practice switching between only playing one hole, and playing chords on multiple holes. This type of playing is called “straight-harp” or “first position.” As you might suspect, the number of holes you blow through is partly controlled by your lips. To allow greater control over the notes you play, you'll eventually learn to use the blade of your tongue to block holes as well. This is covered later. Draw in a breath to change notes. Remembering to pull air across the reeds gently, breathe in to bring each note up a step. By breathing in and out through the mouthpiece, you can gain access to all the notes your harp is tuned for. This type of playing is called “cross-harp” or “second position.” Cross-harp notes are often well-suited to blues riffs. If you have a chromatic harmonica, practice pushing and holding the slide button to further control the notes you produce. Try playing a scale. On a C-tuned diatonic harmonica, the C scale starts with (up) 4 and climbs to (up) 7. The standard out, in pattern is repeated except for on the 7th hole, where it is switched (draw in first, then out). This scale is the only complete scale on a C-tuned harp, but you can sometimes play songs on other scales, provided they don't require the missing note(s) of the scale. Practice. Keep practicing playing scales and individual notes until you're comfortable with playing just one note at a time. Once you can exert that level of control over your instrument, pick out some simple songs and practice them as well. Tablature for songs like “Mary Had a Little Lamb” and “Oh, Susanna” is easy to find online, if you get stuck. Try adding texture by playing multiple notes at once. The next step in your practice is to slightly relax your control and add two-note and three-note chords to the songs you practice by playing two or three adjacent holes at once. This will help you develop more control over your mouth and your breathing, and make the songs more interesting to listen to. Don't play everything in chords! Try adding a chord at the end of a verse or phrase. The important thing is to get comfortable switching between single notes and multiple notes. Pay for lessons. From this point on, though you can certainly continue to teach yourself, you'll see faster and more technically sound results if you practice under the tutelage of an experienced player. Harmonica lessons vary in price and frequency; feel free to try a few lessons from a teacher and then move on until you find one who fits your needs. Even as you take lessons, continue to rely on guides and books to help augment your playing. There's no reason to drop all your other material just because you're supplementing it with professional lessons. Skip holes. It's easy to fall into a pattern of constantly forcing air in and out through your harp, but as you begin to play more advanced songs, you'll need to practice skipping over some holes to reach others. Play songs with notes that require you to jump a hole or two, such as the American traditional tune, “Shenandoah,” which has a jump from the 4th to the 6th hole near the end of the second phrase (on a standard C diatonic). Practice skipping by pulling the harmonica slightly away and then returning it to the appropriate position (to further your familiarity with the position of each hole) and by stopping your airflow without removing the harmonica (to give you more practice with breath control). Play with two hands cupped. To start with, you've probably been holding the harmonica with the pointer finger and thumb of your left (or non-dominant) hand and sliding it as you play. Up your game by adding your right (or dominant) hand. Rest the heel of your right palm under your left thumb, and then lay the blade of your right palm along your left to that your fingers can curl up around your left pinky finger. This creates a “sounding hole” that can be used to affect the sound coming from your harmonica. Add a soft warble or wail by flapping your sounding hole open and shut. Use it at the end of a verse to add emotion, or just practice it anywhere you like. Create a train whistle effect by starting with the sounding hole open, then tapping it shut and open again once. Play a muted, soft sound by leaving the sounding hole mostly closed. You'll likely find that this position forces you to hold your harp at an angle, with the left end pointed slightly down and inward. This position actually lends itself to other techniques as well, so embrace it. Learn to tongue block. Tongue blocking is a great way to roll single notes into beautiful chords without breaking the original note. Using the side (blade) of your tongue, you'll block some notes of a chord, and then lift off partway through the note to add them. This technique takes practice, but your sounding hole position should help present the side of your tongue to the mouthpiece naturally. Start by opening your mouth to cover the first four holes of your harp. Using your tongue, block holes 1 through 3 and play a straight-position note on hole 4. If you did it right, you should only hear (up) 4 being played. Once you can do this with ease, play a sustained note and then lift your tongue off halfway through to introduce the full harmony. Tongue blocks can be used to add a waltz- or polka-like airiness to songs by alternating them with individual notes, or in any of a number of other different ways. They're very flexible. Practice using them until you're comfortable improvising them from song to song. Begin to learn note bending. Probably the most advanced technique in terms of the sheer amount of practice it takes to master is note bending. Note bending is the art of actually changing the notes your harmonica produces by making airflow tighter and sharper. Master harpists can turn a diatonic harmonica into a de facto chromatic harmonica just by note bending. For now, practice using it to produce flat notes to increase your repertoire. The basic technique for bending a note is to make the opening in your lips very very small, and sharply suck air through them into the hole you want to bend. Draw a cross-harp note and gradually pinch your lips together until you begin to hear the tone change. By pinching your lips more or less, you can further control the tone of the note. Be very careful when you practice note bending. Because the air crosses the reeds so sharply, it can easily loosen or bend them, ruining your instrument. Patience and care are required to find a happy medium between not bending a note and bending it too harshly. 
Choose a harmonica. Learn about your harmonica. Learn to read harmonica tablature. Make a note by blowing. Draw in a breath to change notes. Try playing a scale. Practice. Pay for lessons. Skip holes. Play with two hands cupped. Learn to tongue block. Begin to learn note bending. 