I agree with Cheval and JustDressageIt completely! I've seen a lot of people just force the horses head down with side reins or draw reins, without actually allowing the horse to work into a frame and develop the muscle they need in order to carry themself in a nice frame. Is it just me, or does it actually hurt anyone else to look at those pictures of horses behind the vertical?? Those are the type of people that have forced the horses head into a fake frame or have to hold the horses head there. I agree with JustDressageIt about seeing a long and low headset first, and then bringing the horse into a more collected frame. When you first start out, your horse wont be balanced and probably not using they're hind quarters, and maybe even have their head stuck in the air, so starting your horse on a long and low headset helps getting your horse to use they're hind quarters and stretches they're neck and back muscles so you can eventually bring the horse up into a frame.
It takes time for a horse to correctly come into frame, so be patient and good luck!