Back when I was doing steroids I gave myself a lot of injections that were IM.
One thing you haven't mentioned is doing a pull back. Once the needle is inserted, you should pull back on the plunger slightly, and check and see if a lot of blood enters the tube part of the injector - this will mean you're inside of a vein with the tip of the needle, which = bad as it'll waste your shot most likely if it goes directly into a vein.
So, insert in a good location, perform pull back, no or only a miniscule amount of blood showing (pull back is only about 1/4 of an inch or so in the size of injector I was using), and if none is seen, let go of the plunger, it'll return to flush on its own, then press the medication in. Depending which muscle, you can also pinch it from as low as possible when inserting the needle.
Once you figure out good spots that you aren't hitting blood vessels/veins at all with, you can dispense with the pull backs IMO, I never had an issue with 100s or not 1000s of injections over the years back when I was young and foolish (more foolish anyway).