One of the big mistakes that I see is when players think too much about their specific putt and miss some of the major slopes running through the green. How many times have you hit a putt that finishes short of the hole only to discover that you hadn't spotted the gentle slope you were putting up? For this reason, make sure that as you walk up to the putting surface, you take in the general topography of the green. Spot the major slopes, see where the big run offs are and you'll be in a much better position to go on and read your own putt.

Walk it 

When looking at your own putt, if it is long with a significant break, it makes sense to walk it. Feeling the contours in the green beneath your feet will give you a feel for how the putt will roll. Try to build a picture for where the putt will start to break from. This will be your aim point so understanding where that is, is crucial.