Summarize this article in one sentence.
Rise upward and forward simultaneously, and keep your spine straight, chest out, and shoulders back. As you post, lean forward about 30 degrees. Allow the horse’s motion to direct your post; remember to think of your core, hips, and legs as an extension of the muscles in the horse’s back. Don’t propel yourself with your feet or legs. You should only rise about 2 inches (5.1 cm) out of the saddle. Bouncing hard or propelling yourself with your feet can hurt your horse. Your legs should be relaxed; don’t squeeze the horse tightly or use your legs to keep your balance. That said, make sure your calves remain in contact with the horse’s barrel. This will help you avoid involuntary leg movements. If you don’t maintain control over your legs, you could accidentally kick your horse and confuse it. The pressure on your stirrups should remain steady as you rise and sit. Instead of bracing your ankles and forcing yourself upward, move gently up and down with springy, supple ankles. If you’re riding without stirrups, extend your legs and use your seat to balance. Scrunching up your legs can cause you to tightly grip the horse with your knees and thighs.

Summary:
Post forward at a 30-degree angle. Keep your calves pressed firmly to the horse’s barrel. Maintain steady pressure on your stirrups if you’re using them.