What I've found out helps me was opening my hips up. My instructor told me I had very tight hips so I began to do stretches that open my hips up. I just found out last Thursday that by opening my hips up and keeping my upper leg away from the saddle that I sit deeper into the saddle and have more contact through my calves to the horse. Also having your heels down helps a lot. Just relax, take a deep breath. Don't grip with your upper legs.