The Association Croquet pages contain some coaching and playing tips and are intended as a reference for ideas for players to try out for themselves.
There is also a 1-day course on Short Croquet.

MyCroquet GC Coaching website

Golf Croquet Coaching Support

We have played Pirates Croquet at Taunton Deane and evolved
a set of rules for our own use.
They may be downloaded here for use at other clubs.