One could write a book on scouting tecniques. There are quitea few things you're looking for. Some obvious, some not so obvious. First thing, locate food and locate the bedding areas. Feeding areas can be anything from crop fields, clearcuts, overgrown pastures, oak stands, cut overs, etc. Bedding areas can be a pickle to find, especially in big woods areas where deer are more prone to just flop down where ever they feel like it.
I actually like to start my scouting during the winter months, especially during late season. Trails and droppings are more evident in snow and I feel that the deer are closer to fall patterns right after seasons are finished and we get our first good snows in December. You also don't run the risk of blowing up your areas at this time of year. You can be as intrusive as you want since season is almost a year away. Look for bedding areas that a lot of deer are using. Areas where the snow is matted down from deer laying. There are usually droppings and urine there are well. If you have feeding areas such as fields close by, follow trails to them from the bedding areas. Look for the most heavily used trails and make notes on them. If its a buck you're after, remember that bucks, especially the older ones usually don't use these "runways" like the does do until the rut. Then, all bets are off.
During the late summer months, start glassing fields from a distance in the evenings. Watch for where deer enter fields and make notes on it. You might even stick up a few cameras to see what is using those trails at night. Usually, bucks are relaxed and enter fields in broad daylight in the late evenings to feed so its a good time to take stock of what's in the neighborhood.
Once season starts in early fall, try hunting is spots that offers you a good vantage point of several known trails. This will help you make your next move to get in closer for a shot while not putting much pressure on the deer.
Best thing to do is put in the leg work and start walking, and observing. You'll be amazed at how much you'll learn in few outings, especially at this time of year.