Okay, this is overall a really terrible movie. (I am one of those people who watches bad movies for entertainment), but it includes some really good tips for producers who include horses in their picture.
1. Make sure that all of your stunt doubles and any actors expected to ride in the production actually can ride. It is really quite obvious when the horse is actually being controlled by a wrangler off screen with a bag of peppermints.
2. Historical accuracy pays off, it really does. If your story is set in fifth century Britain, then the largest horses available at the time were about 14-15 hands and would have been left there by the Romans. (These horses are the ancestors of the Welsh Cob and other large "native" breeds). If you're a Pict, then the horses you have available are 12 hand ponies. Friesians and Warmbloods look great on screen, but...
3. Same note on tack. Try to use bits that had actually been invented when your movie was set. And having your actors and stunt doubles wear heavy clothing is not actually going to hide anachronistic saddles well enough.
4. If you want a horse to perform an air above the ground, find one that actually can. Or don't bother. Don't try to create one by splicing together a rear and a buck.
5. Don't have your supposedly brilliantly skilled horsewoman do stuff that's obviously unsafe, like galloping along a 45 degree slope, galloping on a tar...what, it's the fifth century?...mac road, going flat out downhill. No skilled rider, no matter how much of a hurry she's in, is going to do that because if your horse falls you ain't getting there any time soon.
So, sorry, bad example today. (The movie got everything else wrong too, mind, including an inability to distinguish gods from fairies. And Vortigern wearing his crown outside his helmet was amusing too. Maybe Richard III should have done that...)
THAT is what your picts should be riding, by the way ;).