So, me personally..I inject pretty high up on the quad. Basically right below the crease where your quad meets your hip. A lot less pain and vessels up there. If you dont like that, try more on the outside. Flex your muscle before you inject and look for the thickest part of the muscle. Then relax and put it in. Also, its a good idea to lube up the needle by squeezing a small drop or 2 and letting them run down the needle. If you get shaky, try using your non-dominant hand, this works for me for some reason, then I push the plunger with my right hand.
Damn dude, are active duty Navy? Not worried about a piss test?