One must remember to hold your hands about one hand's width apart; just above the front of the saddle. Then bear in mind to keep a good grip on the reins without having a heavy hand which will pull on your horse's mouth; this action which will make him/her tense. To counteract this start with your fingers and assure that they are properly gripping the reins. From there the placement of your hands on the reins wil help maintain stable contact without putting the weight on your horses mouth. Working up from your hands, keep your wrists slightly relaxed and bend your elbows to prevent your arms from locking and keep a more natural bend to your arms.
One point that is a good reminder when you feel that you are gripping your reins too tightly, is to turn your wrists inwards just a small amount which will allow a more gentler hold and gives more for your horses mouth.
Keeping these tips and advise in mind while hacking, in a lesson or in competition, will assist me and other riders in the future to have an amazing ride. In the end, don't forget the importance of your hands. For a great refresher you can always refer to George H. Morris's book, Hunter Seat Equitation Chapter Two: The Rider's Aids, page 29, which discusses the topic more in depth.