Its hard to explain how to get the best out of your horse on here as setting up a horse to show off his best conformation features is hard without actually seeing him in person. At home what I like to do is set my horse up and figure out exactly how I would like to stand him in the ring. I use a big mirror so I can see the side of the horse at about where the judge would see - your view and the judges view is much different.
If you don't have a giant mirror, you could get someone to help you - they stand the horse up and you look from the judges perspective.
After I stand the horse up, I run my hand along his back to make him relax it. Its such a subtle thing that makes a huge difference in the overall picture.
To make him 'use his head', its hard to explain but basically, I think it as, up and out. Meaning, don't just get him to stretch his neck up so the underneath muscle is showing (ewe neck = conformation fault) or don't just get him to stretch his neck straight out and low. BUT in saying this, if he has a naturally built ewe neck, this is partly how you can help disguise it.
Now, when getting a horse to use his neck, he must stand how I want him, I then get his attention, thus he raises his head (and neck), then with a treat (or something yummy smelling) I get his attention then he will stretch his head out = up and out. Do not let him nibble at you or step forward or stretch too much.
This is a basic way of looking at it but, I think you need to get a mentor who's happy enough to help and has a lot of experience in miniature horse showing, that can come and see you and your horse in person to help out. I would, but I live in a whole different country.
Conformation comes into play so much here and I personally think you should study up on it and give your horse a fair evaluation.
