Well, to start out if you wanted to go to the show, there are a few things you can do. Then improve from there as you watch and learn.
Conditioning is the most important for a halter horse. But as you work them, get them to set up. The front legs should be a nice line with their shoulder and their back legs not stetched behind them. You can touch a horse's legs to set them up, but I find it is hard to do that when the judges are walking all around. So I just teach mine to setup. Make sure they know how to whoa with lots of commotion and you not being directly in front of them. You don't want to be in front of your horses nose, but at least a foot of so in front of them. That way you aren't "crowding" your horse when you ask for a stretch (something I learned after my first shows). When you ask for a stretch, you want their head to go up and out. Not down. If you ask too much, then you'll gator their neck. You can kind of look at magazine pics and have someone watch you. But its a learned thing you'll do later when you get to know your horse. Sometimes your horse will want to stretch forward with their body. You don't want this. You want them to stretch their neck with their head, not their body.
It all comes. Hope it helps.