1. The most important rule in horseback riding is.... KEEP YOUR HEELS DOWN!!!!!! Why?? Because not only does it make you more secure, but it also stops your foot from being caught in the stirrup should the horse spook.
2. The second most important thing is.... keep your head and shoulders up and sit straight up and down or lean slightly back. This puts you in a secure position for riding. For instance, if your horse were to buck and you were leaning forward, you would find yourself on the ground.
3. If the sport you choose to ride in requires speed for the most part (ie: eventing, games), it is best to choose nylon-backed stirrup leathers (for english saddles) as these can stand a lot of wear and tear and are almost unbreakable.
4. If you horse is going strong on the forehand or is lazy, you might want to try leaning back a little with your shoulders behind the perpendicular. This will make your seat stronger (as long as your legs stay in the correct position) and push your horse forward into better movement. But Beware... don't overdo this as it may put strain on your horses back.
5. DO NOT WEAR JEANS when you're riding english. Western is okay...but not english. They make you slip extremely easily..especially on a leather saddle and the seams can be very uncomfortable. Riding breeches are best because they are designed for riding.
6. Some horses are troubled by riding through water. Having a friend ride a calm horse through while you and your horse watch will show your horse there is nothing to be afraid of, or gently leading your horse through the water if it isn't too deep can both help your horse overcome this problem.
7. I strongly advise anyone wanting to get involved with horses to take riding lessons with an instructor. When I first started riding, I didn't have lessons and therefore adopted an incorrect seat - that was 6 years ago - I'm still working on correcting that fault. Riding instructors will teach you proper riding techniques, ground handling, etc... that will benefit you very very much! Please take the time to read my "Finding a GOOD Riding Instructor" page.