Needles are more likely to bruise the slower you go or the tenser you are.....easy to say relax, hard to do as a learner driver. Also if you are hot you have more blood vessels closer to the surface and therefore more likelihood of nicking a vessel. straight in with a steady motion not stop start again hard not to do when you are nervous. You will also find the angle of the dangle has a part to play. The needle is filed away to a point but only one the one side if you get what a mean. If you have that side or more exactly the exact part ot the point going in first the insertion will be cleaner. So if you find you inject on a slight amgle check that the eye where the drops come out is facing up towards you. This will ensure the pointiest bit is puncturing the skin more cleanly. OH and most importantly...remember to breath. So Many people hold their breath when they inject, this will only make any pain worse.

Good Luck