Greens are relatively flat and smooth surfaces. The grass is short. The ball sits up high. So, making solid contact with the putter should be easy right? Wrong. This is because the problem that people run in to when putting has less to do with the external factors (the green, the ball and the putter) and more to do with the golfer. If making good contact on the green is a problem you face, the best way to work through it is to start on the practice green.
Difficulty: Moderately Easy
Start on the practice green. Bring up at least three balls, more if it is not crowded. You'll want to start with short putts, 3 feet or so. Set your balls in a line and knock down one putt after the next. Do your short range putting three times focusing on your stroke as you pull back, make contact and follow through.
Move back to 10 feet and run through your balls three more repetitions. At this distance, you'll find that body alignment becomes much more important to the travel of the putt and its eventual resting place. From this distance, you'll get a better feel for what makes solid contact and what doesn't. Keep your body level, swing through the ball and make sure that you follow through with the head of your putter. At 10 feet, the tendency is to try and drain the putt, but at this distance you should be working on getting the putts as close to the hole as possible.
Go out another 15 feet to a distance of about 25 feet. At this range, your body position and stroke will be even more noticable in the final outcome of your putt. Read the slope of the green from where you are putting from. Once you have read the green, line your feet up so that if you ran a line from your back foot, past your front foot and on toward the hole, the tips of your toes would line up with where you want the put to go. Stay low through your swing. Focus on controlling how you bring back the putter. Make sure that your swing is smooth (without hitching) from the pull back through contact and your follow-through.
Swing in control. Keep your swing within a certain perimeter. No matter how far you have to put the ball, you should never have to draw back more than 12 inches from the ball. By keeping your back swing short, you'll bring some control to your stroke. Then it is just a matter of staying low and following through.
Tips & Warnings
Always practice hitting through the golf ball. This will smooth out your stroke and contact will be more solid.