RE: Squirrel practice.
I use a Ruger 22 pistol with iron sights. They work fine for the 20 yard shots that I am used to dealing with. It might be a while before you have the marksmanship for hunting with a pistol, but if you don' t have a scope on your 22, don' t worry, regular sights are fine. If it is further away than you can hit, either stalk closer or don' t take the shot.
The other poster was right though, practice while holding your gun the same way you would while hunting. Don' t sit at a table and put your gun on a rest to practice, you won' t have any rests in the field. Practice while sitting, leaning on trees, kneeling, leaning back on something, etc.
Good luck,
Chubber