Here is a circle putting drill with a recommended numbers of putts. If you have access to indoor outdoor putting greens it would be ideal for practice whenever you have available time.
You can modify the number of putts as you like. It is generally suggested to start by trying to make a few putts in a row, just to get your baseline. Then, as you improve at the circle putting drill, gain confidence, then you will naturally want to increase the number of consecutive putts you make.
Phil Mickelson’s Circle Putting Drill
1. Find a flat area on the your practice putting greens.
2. Arrange 10 balls in a circle around one hole, each one three feet from the cup. Most putters are just shy of 3 feet of a shaft length, so your putter is probably a good guide for measuring the 3 feet.
3. Start making those putts, working around that circle.
After you’ve made all 10, put down 10 more. Continue the process until you’ve made one hundred 3-foot putts in a row.
If Mickelson misses, he starts over.