I know the feeling... I'm ALWAYS nervous about getting on a green horse for the first time. Just make sure you're prepared and attentive to how the horse is reacting. Swing up but not all the way over, lay over the saddle, and study their ears/body language. The horse will tell you when it's ready. PS... wear a helmet... I don't usually when I ride, but when I'm backing a youngster for the first time (especially in a roundpen or somewhere where they might panic and throw you into a fence) it's a good idea.