Take your time
Keep that same pre-shot routine as you would on the course. You don’t get bonus points for hitting all the balls in x-amount of time.

On the green
This may not be an option at a range, but certainly it is prior to heading off to the course is to spend time on the practice putting green. Don’t just practice long putts. Try making those that are 3 feet and in by dropping a few balls around the hole. Once you can make a high percentage of these, then you can practice those 10-footers.

Read a book
If it is raining or cold outside, what better way is there to practice improving your game?