Answer

By Your Horse

YRC Instructor Alison Ritchie advises:

I think you are wise to start at a local level and it would be a good idea to visit a few different shows to get a clear idea of what different classes entail. There is certain etiquette to follow, both in terms of dress for you and your horse, and a structure to each class. By watching these classes, you will see what goes on, and get a good idea of what types of horse do well in each class and, therefore, which class might best suit you. You might also be able to chat to some of the judges, again to get a better insight.
There are many books available that cover various aspects of showing, so visit your local bookshops, saddlers, or browse the internet to find the best ones to suit you.