In Ohio, you can stalk and hunt quite effectively in the early part of the season. Later in the season after the foliage has dropped, it becomes virtually impossible to make your approach unannounced (unless the ground foliage is wet). This time of year the ground foliage will be frozen which makes the sound of your approach even more pronounced. You may see a squirrel take off in the distance, only because he's seen (heard) you first and is therefore quick to skedaddle (which is the case for any number of game species). As mentioned above, find a comfortable location and once your situated, be still. I usually give them 20 to 30 minutes and if there's no activity will move to the next location.
Other than being in a wooded (deciduous or pine) area, there's a couple of things you can look for that could indicate their presence. Tree nests made of leaves and twigs are easily identified now that the foliage has dropped. Eastern Tree Squirrels build tree nests in the heat of the summer to stay cool during the night. They won't be using tree nests this time of year, but their existance are a good indication that squirrels have recently made the area their home.
Also, it pays to know your trees. A large part of a squirrels diet is made up of nuts (walnut, hickory, beech, oak). If you find a patch of hickory, walnut, or beech trees, good chance squirrels will be hangin around. If in addition to nut trees, you spot tree nests from the previous summer, good chance you've hit paydirt. Then there's always the issue of whether or not they decide to emerge, ...that's another story. Suffice it to say early morning or late afternoon are the times of greatest activity, but I've spotted squirrels out and about during just about any time of day. --Don't go during heavy rain. Squirrels don't like it and neither will you!
Here's a couple of tree types you should become familiar with:
SHAGBARK HICKORY
BEECH
This time of year can be tough. Squirrels don't hibernate, but they will bed down for several days (or just come out for shorter spells) during extreme cold temperatures (low teens or single digits). A short absence of food does them little harm since they've fattened up nicely during the fall mast season.
As with all hunting, don't measure your success in number of kills. Experience, and a gradual learning curve will produce much greater long term dividends. In the mean time, enjoy yourself.
Good luck, and good hunting!