That's a tough question, cowgirl! Mainly because there's SO much to do!
First, you should set up the basic rules - a good foundation system can help, for example, the parelli lvl1 or something alike, that explains to the horse how you ask direct and indirect yielding, in order to perform circling, backing up, accepting different kinds of pressure, etc. That shouldn't take you longer than a week or couple of them, so that the horse doesn't get bored. Also, you have to learn to use precise body language and focus on using your energy and body more than any tack. A good comprehension for both the handler and the horse about what is personal space is also a must.
We move up from there just as in riding - in order to achieve collection one day, we first have to work on rythm, balance, contact. Also, the horse has to trust the handler completely and be relaxed and willing to do things with the human.
I like to start with the simplest things. Spending time in the pastures and doing nothing, observing the horses and waiting, until my horse comes to me. Then I offer following me around, offer the halter to be put on (and respect it, if the horse shows that he doesn't want all of that the particular day!), do some leading and go for long in-hand walks down the trails, in which we work on/"talk about" being light to the pressure of the halter and respecting each others' space, myself being focused so that he is interested to follow me and we then graze where I show it's to be done - just as a lead mare would do. The result should be effortless walks, in which the horse stays light, happy, focused on me, ready to go over any obstacles. There we can also do in-hand trotting hillwork, stretching long and low in trot, doing walk-halt, trot-walk , trot-halt-trot transitions, sidepassing over logs, climbing with forelegs on treestumps, flexing neck, arching back, backing up, lunging with encouraging to use the hind legs more, and doing other exercises that support the suppleness of the horse and that prepare him for the collection. I always suggest, not command, and I try to make everything short, fun and sweet, so that the horse feels rewarded even by just being given the chance to do something with me! In the arena, we can do cavaletti work, the Spanish walk (to encourage good shoulder action), etc., and also ground driving is a very good thought, as it can help with working on light contact, straightness, flexing and more. Also, I always remember to spend as much or more undemanding time with the horse, as I spend in doing something with him.
Overall, the collection cannot be taught, imo. We can help their bodies and minds to evolve, we can support their energy, personality and pride, and then, one day, the collection starts coming naturally, as a result of the horse being fit and ready enough to present it to us.
Being a larger, slow growing horse, who is inclined to be on the front and lacking impulsion from the back, this is what he is offering me now. Still work in progress, of course -
I would highly suggest that you do some reading for inspiration. This is what has greatly helped me in the way and given me some valuable ideas on precise exercises or techniques -