Beginners normally like to simply walk up to a putt and attempt to hit it in. It is more efficient to have a short pre-shot routine for your putts. There are several different ways to approach this, the important thing, if you are an amateur, is to keep it short.
As you walk up to the green, look at the way the green slopes, and imagine what you think is the natural break in the green. If you envision how water would flow downhill on the green, that can make it more clear. A simple approach is to stand behind the ball, looking towards your target. Picture in your mind how much you think the ball will break as it rolls towards the hole.
Now stand over your ball. Look at your ball, then the hole, and back to your ball. Picture the ball going in the hole as you pull your putter back, and strike the ball. Now watch the ball, hopefully it went in, but if it did not, look at where it stopped and how it moved in relation to the hole. If you are on a practice green, hit another ball until it goes in the hole.
And always hit the ball in the hole, no gimmies. Putting represents over 40% of the strokes you will make during your round, so it is worthwhile to have a consistent, short, and effective pre-shot routine for your short game. It will definitely pay off.