Sterile technique is the fundamental here. Open fresh alcohol pad and wipe the vial stopper for 10-15 seconds. It is now sterile. Open needle package remove needle cap. Aim thru the center of the sterile stopper, invert & draw. Obviously, don't impact the bottom of the vial with the needle.
Draw the product to correct level. Aspirate any air bubbles, wipe injection site with alcohol pad 10-15 seconds and inject.
YOU CAN SWAP NEEDLES IF; USING MULTIPLE VIALS OR YOU'RE SENSITIVE TO PAIN. There is no sterility issue, however.
I 've just used one needle most of the time and have hundreds of injections under my belt and never any issue. (23 gauge 1 1/2" needle in 3 ml syringe)
The needle remains sterile as long as you don't touch it or lay it down. The contents of the vial are sterile so as long as stopper has been properly wiped, needle stays sterile.
YES it does slightly dull the needle but it is still plenty sharp to pierce the skin, it does hurt about 10% more than a virgin needle, but that's nothing compared to the gym.
ps I have been injected by doctors, never once saw them waste a needle...