K22: good point. I might add that lower-power scopes, such as, say, a 3 x 9 power won't need parallax adjustments. I use a higher-power scope, however, because a higher-power scope just works better for me. For squirrels, I don't feel that anything above 12x or 14x is required; Besides, these types of scopes add weight and, as you mentioned, will require parallax adjustment. Nothing wrong with a 3 x 9 for those closer 50-75 yard shots.
I had been using 40 Gr Power Point ammo by Winchester n my Ruger 10/22-based Clark Special, but there were a few jams, and the accuracy was not as good as the newer 36-grain HP 333 ammo by Winchester. The 333 OAL is a bit shorter than the Power Point (same case length, shorter bullet length), and since I have been using it, I get a flatter trajectory, the ammo is very accurate, and I get no jams. They sell it in boxes of 333 for around $14 at Cabela's. I now use the Power Points in my Ruger 77/22 with no problem.
Dave, as was mentioned by another poster, I would find out which ammo works best in your particular rifle. My own opinion is that a 50 yard zero is pretty much a good starting point. That way, you can always adjust easily for shots under as well as over 50 yards. Don't count too much on shots of 100+ yards, though, unless your rifle is super-accurate and unless there is no wind. I have made kills at 130 yards, but most of my successful shots, however, are at 75-yards or less.
But, if you are hunting in timber, etc., as you say you are, you might want to zero for closer shots. In open country, however, I would set the scope up for 50-75 yards, but that's for my rifle with my particular type of ammunition. Best thing to do is pick an arbitrary distance, set up for that distance, then adjust up or down. Write down the bullet drop figures on a piece of paper and tape it to your stock so you won't have to guess where to set the scope or where the reticle should be placed.
Personally, I used Kentucky Windage for my shots and have no problems, but then again, I might shoot a brick of .22 cartridges during a day's shoot, and I pretty much know where the bullets are going to land without having to horse around with changing the elevation or drift stuff on the scope.