Decide how thick you want the coat, or determine the type of finish that you want (from completely smooth to rough and textured). If you are right-handed, you will be holding the skimmer plate in your left hand and the compound applicator in your right hand. You may have to adjust your technique to get the desired thickness and texture. You can always add more compound to the surface, but once dry, it is messy and time-consuming to remove. Mound the compound up at one end of a repair area, then pull it across the surface with the compound applicator. Apply firm, even pressure in the direction of the joint/crack, similar to pulling a window squeegee, such that little material is present on either side of the repair area.  Start in one corner of the wall, and work down from the highest point. If you are skimming a ceiling, start at an edge and work towards the center. If you have never skimmed before, try practicing on a piece of scrap drywall. This way, you can get used to the applicator and the weight of the compound, and you can see what it will look like when dry. Once you have applied the first scoop, take another and work out of the spot you just finished. Be thorough—make sure that each new scoop overlaps with the last. Pull the coat in different directions to even out bumps and valleys regardless of how they are aligned.  A repair area isn't flat: it is a low, smooth mound, made to look flat. Shine a light along the surface to identify areas where the wall is sunken, and mark those spots with pencil as you go. Patience is key, but you must work efficiently so that the mixed compound does not dry out before you finish. Give yourself enough time to complete an entire section. Try not to stop in the middle of a surface, as blending a dried section with wet compound can be difficult. Do not try to rush the application by taking a larger scoop. This may make your arms tired, it may lead to compound falling off your skimmer, and you may need to go over the area later to remove excess compound. Smooth fiberglass repair tape onto cracks and joints. Let the surface set or dry out before you apply the next coat. If repair areas are deep/large, count on 2–4 coats to get solid repairs & smooth surfaces. Do not apply excess material or try to finish with one coat—this can only be fixed by demo or lots of sanding. It is better to do many thin coats than an uneven one that needs repair.
Prepare to apply the first skim coat. Apply the first scoop. Keep spreading the skim coat over the repair area. Allow the first layer to set for several hours or overnight.