The two big variables on the green are the speed and firmness of the turf. Focus your pre-round practic e on getting a decent feel for pace before becoming target-oriented.
Don't putt to the hole
All putts are speed putts, because you have to know the speed of the putt to control distance and gauge break. The proper pace becomes instinctive on your home course, but if you play somewhere else it's easy to get thrown off track. Before your round, practice putting to nothing, and feel the pace of your putts by hitting uphill, downhill and sidehill.
Control the length of your stroke
The average golfer should concentrate on getting long putts within a six-foot circle around the hole. You tighten those parameters as you progress--just as you're trying to expand your tap-in range on short putts. If you're trying to break 100, your goal should be to get a 20- to 30-foot putt within three feet of the hole.
Practice lag putts from just beyond what you feel is your automatic two-putt range. Focus on swinging the putter to even lengths back and through, with the same steady pace throughout the stroke. Feel the length of stroke you need by swinging the putter over the ball as you're looking at the hole, your eyes over the target line (left). Get a feel for speed before worrying about the break.
Measure and practice your the golf course's practice green before you play! 
Measure the practice green and compare to your standardized putting stroke. Practice until you have made the proper adjustments to compensate for any differences in the green speed. 
