Bro,
Quad injections are the easiest, IMO. To find the right spot, place your hand flat against the top of your leg where it joins to your hip. You want to shoot just below where your fingers touch your quad an inch or 2 outside from the center. That area of your quad usually feels somewhat flat, so it is relatively easy to find. There are more nerves in your quads then in your glutes, but it is still not likely that you will hit one. Also, if your legs are no too tan , you should be able to see the blood vessels directly under your skin so you will not pass the needle through one of them. What type of pins are you using? LATE