He gave me two drills to work on that I thought were great, so I thought I'd share them here.
1) Pick a spot on the practice green where you'll have a straight putt. Place one tee at 3' out, one at 4' out, and one at 5' out. Starting at the 3' tee, make 5 putts in a row. Once you do that, move to the 4' tee. If you then make 5 in a row from there, you need to make 5 consecutive putts from the 5' tee. If you ever miss a putt, you must start all over at the 3' tee. The idea is to take out the variable of break, so you can concentrate on alignment and mechanics. Also, if you can get to a point where you can easily complete this drill, you should become really confident when you face similar length putts in a round.
2) Practice lag putting by, at worst, two putting 5 consecutive 20 to 40 foot putts. Pick your distance and putt 5 balls from there. After that, you must hole the next putt from wherever each ball ended up, or you have failed the drill.
In his opinion spending a sizable amount of putting practice on intermediate length putts (10 or 15 feet, let's say), won't lower your scores.
I thought I'd share these ideas as I think they make a lot of sense. I would be interested if others agree, or think there are better ways of practicing (I know there are a million different practice routines to choose from...).