To determine the best area to inject in the quads, imagine a line down the front of your quad from your hip bone to your kneecap. Divide it into 3. Take the middle third.
Now imagine a line from your hip bone down the side of your leg. Divide the area between the front line and the side line into 3. Take the middle third.
You now have a letter-box shaped area on the outer quarter of your middle quad in which to inject. This is where the quad muscle belly is fullest.
If you imagine injection sites as 1 inch diameter circles around the needle entry point, you have room to do from at least 6 to maybe 12 injections, depending on your quad size.
So alternating between your two quads you should have plenty of sites to use before you return to the first one. This will give any scar tissue ample time to disappear.
There is no need to go into the quad deeper than an inch, in order to avoid deep nerves, lymphatic and blood vessels and the bone.
To inject, sit on a dining chair, position your lower leg at about 45º to your thigh so the quad is fullest, and keep it totally relaxed.
After swabbing copiously with antiseptic (Listerine), slide the needle in slowly and smoothly, and be sure to aspirate, as explained in our stickies in injecting.
After injecting, massage the area well to ensure the gear is dispersed. It is best not to inject before bed, and good before a workout in order to keep the quad mobile, which will aid dispersal and minimise PIP.