Around here they keep shockingly regular hours from one day to the next, obviously make sure you there early in the morning when they're first coming out.
I always knew they were vocal animals, but I had no idea that those 2 dozen or so 'forest noises' that I always just assumed were some bird of some kind or distant rabbit or just gust of wind was actually all coming from the squirrels. Some of them refuse to ever shut the hell up, either in alarm or to give the all clear, or to keep other squirrels out of there territory. Use this to your advantage.
If your convinced that hey always just happen to climb the side of the tree opposite from you no matter how bedded down and out of sight you may think you are, its not a coincidence. I find them very receptive, not always hesitant, and not always curious just receptive to anything foreign that they come across. We always throw a couple pieces of clothing or a jacket or whatever on the far side of where we know there going to be munching on breakfast which genereally tends to spin them around to us.
Ive only ever shot the little suckers with pellets my entire life, and Im not certainly not any type of incredible rifleman, but I find heads shots not being terrible difficult to accomplish. If im close enough to to one I am generally close enough to take it. I almost wonder if going out with a .410 or 20 gauge like many people do might actually be more difficult in some strange way.