The Principles of Riding is a really good handbook for dressage, but might be a little tricky to understand at first. Cross-Train Your Horse and Lessons with Lendon are both good dressage books that are a bit more beginner friendly.
For jumping Hunter Seat Equitation by George Morris is very good. Oh, and the 101 xxxxx Exercises books are very good too.
Also, I agree that British horse magazines are great.:001_smile: