My method:
Begin by drawing the plunger of the new syringe back a few units, then
push firmly to the needle. Hold it there while inserting the needle into
the vial. This insures you are starting from 'zero' and with no air already in
the syringe.
Draw dose and a tiny bit more....guesstimate based upon how much air you think
you have to compensate for.
Remove syringe from vial, and now draw in a tiny bit more air...2-3 units.
Hold the syringe horizontally, and tap the area with where the air is trapped with
a firm object, like the handle of a table knife. The idea is to get all the
air into one bubble at the tip. I find using an object rather than your finger
is more effective (sharper tap).
While continuing to tap, slowly raise the needle end until it is pointing to the ceiling.
The air should collect at the tip.
Now expel the air and any excess insulin to your desired dose. If the dose is too small, you
can insert the same syringe into the vial for more, and repeat the process if you have to.