Deep breaths and relax, we do not stay on by tensing particular muscles, just like it was said before enjoy yourself and don't think too much about it! If you tense your thighs or calves your legs will bunch up as you will be gripping with your knee's and you will bounce and it won't be a lot of fun! Just relax and remember to breathe - the tip of singing a song is a good one!
Your question earlier about where the book was on the classical riding website - check out under the merchanise tab
CRC - Invisible Riding
If you really want to watch other people - try searching on you tube or better still go to some local dressage competitions and watch. It always helps watching other people riding!
Steph
Paws Of Eskbank