I’ve been trimming my own horses now for about 4 years. In those few years I’ve been through a couple different methods, finally settling on one that has worked wonders for my horses. (They started off with cracks up to the hair line in almost every hoof – it was really bad. A few abscesses too. Now they have solid feet, completely sound on grass or gravel.)
The method I definitely recommend I learned from a book by Pete Ramey “Making Natural Hoof Care Work for You”. This is an awesome how-to book. It really explains why to trim that certain way too. The book also explains how to trim horses that have very different feet from each other.