Place your two swing arms slightly inside the edge of the hole, as shown, basically reducing the size of the hole fractionally. Now hit a series of putts from 1ft, 2ft, 3ft.... You can, of course, vary both the width of the hole and length of the putts. After practising this drill for a while the hole will seem huge on your next round of golf!
This drill can be done anywhere and you do not necessarily even need a hole, just use the swing arms to simulate a hole. Improve putting now!