One of the things that makes golf so challenging, and often frustrating, is that greens aren't flat. Every one has some sort of tilt to it so it can drain after rainstorms. Beyond that, there are various bumps, knobs, and valleys that invariably find their way between your ball and the hole.
If you've been good enough or lucky enough to be closest to the pin when your group hits the green, you'll have the advantage of being able to see how the other golfers' shots react to the green.
There are a few other things you can do to prepare for a course. Before the round, try asking a grounds attendant about the general area.
Greens usually follow the slope of the land as a whole. If there are mountains to the west, chances are most greens will slope away from them.
If there are bunkers nearby, the architects will have designed the couse so that water will drain around them.
When figuring speed, consider the grass itself. The broader the leaves, the slower the green. Bermuda is slower than bent grass. Damp grass is slower than dry. Like many plants, grass leaves will point toward the sun, moving from east to west as the day passes.
Putting with the grain is faster than putting against it. Reading a green is never an exact science. The best plan is to play the same course several times until you get the feel of each green.
