You'll be able to come up with more interesting and varied notes for your solo if you base your solo off chords. Chords change much more frequently throughout a song than keys, meaning your chord based solo will likely have a greater variety of notes than a key based one.You may want to go through your song and write the chords for each bar of music if this information isn't already there.
 Now that your chords are written out, you can play scales or arpeggios in the key of those chords to create a complementary sounding solo. When the chord changes, change the scale or arpeggio you are playing to match the key of the new chord.Keys with the same number accidentals or keys different by only a single accidental on the Circle of Fifths are generally harmonious., You can think of the root of a chord as its most central tone. By playing the root of the chord throughout your solo, weaving it into scales, arpeggios, and more, your solo will sound more tonally centered and harmonic.The letter name of each chord generally indicates its root. For example, a Gmaj7 chord has a root of G, an F#min chord has the root of F#., Voice leading is a common soloing technique. It involves playing a note (or notes) either a half or whole step away from the root of the next chord, before that next chord is played.


The notes surrounding the root of your next chord will resolve to that root. When you play the next chord, this technique creates a natural kind of transition between chords.
Break your song into chords.
Solo by soloing according to the chord.
Emphasize the root note of the chord in your solo.
Voice lead into the root of your next chord.
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