Tips for training a young horse to collect?

Under the saddle, mostly, but if anyone has tips for collection on a lunge line that would be much appreciated. I ride English, but I'm temporarily using a Western saddle (although an English bridle and direct reining) because my horse is young and was mostly trained Western Pleasure. My horse is 5, and good tempered but can be stubborn. He is not particularly spooky but needs a lot of exercise to keep him on good behavior. I have walked/trotted/cantered and I got him a little less than a year ago when he was four. He has a very quick trot and canter though and I want to collect him more than just using my reins to slow him. I do work about once a week with a trainer so any advice I will check with her first, and don't worry, I am being responsible so no need to tell me to seek help. I've got plenty of resources.