One problem is that we new riders lack the riding vocabulary to understand books designed for skilled riders. Enlightened Equitation itself (one book which was was beyond me) with her use of bits, redesigned saddles and sophisticated dressage training is not applicable to basic RS beginner lessons and horses where you use what you are given. I believe that Heather Moffet later wrote an e book for new riders. I have seen it mentioned recently and it could possibly be available, I would email and ask her, or you can find her via Facebook Enlightened Equitation.
If you are in the UK, I used the Pony Club handbook for easy reference. The handbooks that go with the Stage 1 British Horse Society exams would be good too. But I also got hold of a brilliant USA book by a British Riding Instructor, Michael W.Smith, Getting the Most from Riding Lessons. It was a wonderful book because he described lessons at various stages of learning and on a variety of horses each suited to the lesson content -
If you are a new RS student and handling horses on the ground and interested in the psychology of showing them what you want them to do, then I suggest Kelly Marks Perfect Manners - How you should behave so that your horse does too. I started riding b e fore it was published and used her earlier leaflets.
Dont forget that these days there are lots of vids on Youtube showing people riding and handling horses. I bought a lot of videos and went to as many demos as possible. I think my brain works by mimicking what I see other people do. There are many situations that for health and safety cant be reproduced in riding lessons. If you can find an opportunity to watch the most skilled trainers at work handling horses, seize it even if you are beginner. I rarely open any of the UK books I have but the images of trainers I watched handling ignorant, rude or recalcitrant and fearful horses are there fresh in my mind.
The American trainers Buck Brannagan and Mark Rashid are both going to be in UK this summer. Michael Peace and Richard Maxwell are other trainers I like to watch.