Whether you are Tiger Woods or a 25-handicapper, the putt you want to have is an uphill one. When your ball is moving uphill, you usually don't have to worry about a subtle break sending your putt off course. Your primary concerns should be your aim and hitting the ball firmly enough to get it up the incline and to the hole. To "read" your putt, crouch down behind the ball and study the line to the cup carefully. Walk up to your ball, take a practice stroke and putt it into the hole.
Downhill putts require a deft touch, a keen eye and the ability to read breaks in the green. You also have to try to judge the speed of your putt. If you don't judge the speed correctly, your ball will either roll well past the hole or end up woefully short. The key to reading the green is to walk the path your putt will take. Factor in any subtle breaks or bumps in your line.
A sidehill putt is a combination of a uphill putt and a downhill one. The low side of a sidehill putt is the dominant factor you have to consider. Get behind your ball and try to determine where the uphill portion of your putt ends and where the downhill portion starts--or vice versa. Hit the ball hard enough so it at least reaches that spot. That should be enough to get your ball to the hole.