I generally start getting a horse back into condition after a lay up by ponying. If that is not possible, then I start by walking. Depending on the injury and the severity I may be careful to pick easy ground, or not.
When the horse can handle a couple hours of that with no ill effects, I may introduce trotting, and increase that as the horse shows me it is able.
It's really hard to say without knowing the whole history of the injury and the horse's general condition and conformation. But the above is just a general idea.
Good luck. Hope your horse is completely recovered and has no further trouble.