Look 10 feet left of the cup and 10 feet right. Determine which side is higher and favor that side. That's the basics. Remember the ball will roll wherever rain would flow to. As you get better at putting, you'll get better at reading, too.
When you miss left/right, is it a push, pull, etc.? Or are you aligned the wrong way? Or is it simply making mistakes while reading greens? It makes a big difference, and an answer to this would help us help you.