I second this advice. The only thing I would add is to only practice putt for 10 to 15 minutes at a time. Any more than that and it is difficult to stay focus and you don't want to practice unfocused putting. Easy way to develop lazy habits. Also like Zane pointed out, just make putts. Doesn't matter how far out, just make putts. While my putting is far from perfect I have taken huge strides simply by being more consistent from 25 feet and in.