Are you at a boarding barn? Make friends and ride with them. If there's a group of people, talking, laughing just walking around the ring your tension will melt and you will "forget" about the scariness of riding and just enjoy it. When you ride alone you can easily mentally psyche yourself out and your horse is more likely to react to your tension. If there are other horses around your horse that are calm and happy, even if you're tense they probably will ignore you for the most part and just follow along with the "herd". Also, just getting on and riding once or twice around the ring and getting off will help you build confidence. If you ride for 5 mins one day you will say, well that wasn't too bad and kinda fun. And then the next time you might ride for 6mins, etc etc etc. Also, give yourself a goal and stick with it. Say, I'm going to ride once around the ring. Or I'm going to go over to that post and back to the mounting block, etc. If you give yourself a goal to think about other than staying on the horse you start to focus on that and you relax. Good luck and keep us posted!!