As with 2Thick and Pitbull's replies they are spot on. I do however also inject into the outerhead of the bicep. Follow pretty much the same procedure i.e. find the peak and then inject.
When injecting the outer head make sure you are sufficiently over the area that seperates the heads of the biceps.
I only inject the thicker AS in to the Bi's (have never done Winstrol - although this is just personal preference and has no scietfic reason)
I have injected 1ml into each head on the same day and my arms handled it ok, but generally only 1ml in either head on seperate days.
Depending on the size needle, make sure that you don't hit a vein or a nerve. (altough it is a bit tedious I use insulin syringes or one slightly bigger)
I normaly inject on the day when doing arms, about 1-2 hours before. Reason being that there is a large flow of blood to the area as well as the extreme pump I get.
Site injection w.r.t arms have definitely increased their size. They are at 20' now.
Hope this helps.