I'm going to go ahead and disagree with some things said above. First of all, a typical dressage headset is not a "swan-neck". A swan-neck is the result of a pulled in neck broken at the 3rd vertebrae.
What we want to think of when we are riding is not riding forward, not riding in a headset, but riding in balance. A balanced horse is a happy horse, and it is when we try to achieve a frame through either pulling our horses into one, or running them into the bridle that our horses become unbalanced and unhappy. Yes a balanced horse is one with a forward thinking stride and he will carry his own head and neck, but we do not create balance through the application of these two results.
In order to achieve balance, we must first ride our horses in a correct stride. They should be absolutely rhythmical, like a clock or metronome and they should feel as if they are taking you forward. Never push. Ever. It is almost as big of a sin in riding as pulling. The horse must go forward from your leg and you must never ever push or pump in your seat, back or leg. Then you just shorten your reins with a soft, steady arm to create contact. Keep your elbow soft, and stay toned in your back with your shoulders back. Never pull back. Create the movement into the bridle and let the horse find the contact, the stride and the frame absolutely naturally.
The best analogy I have stumbled upon is to think about making the horse's spine longer. Just 1/16" at a time, slowly make it longer and longer, and through this length of spine the horse finds his balance.
I would highly suggest finding a good trainer in your area and taking weekly lessons, also taking lunge lessons on a schoolmaster will help you develop your feel and teach you the feeling so you can teach your horse. Keep up with your reading and audit as many dressage clinics as possible. Learning dressage is a very long road, good luck :)