If you want small trees, select plants that have a single strong upright leader. If they don't have that, you will have a harder time.

Prune them lightly, but frequently. You want to remove the lowest branches while they are small to encourage the vertical growth, but don't prune out more than a few every month or you will stunt the growth.

When you have the lower branches high enough so you can walk under the tree, you are into maintenance mode and just prune branches to maintain the tree shape: branches that cross through the middle, branches that rub together, and any that stick too far out.

Make sure they are far enough from the house that they aren't damaging paint, and have room to spread.