When I condition a horse out of work, I typically start with building back up the horses stamina then move on to flexing.
I will walk 2 miles, long trot 2 miles, walk 2, canter 2, then back to a trot for another mile, then I walk for the rest of the ride. I ride 5-6 days a week, so I'll do this 4 to 5 times a week.
I will then move on to sidepassing, backing, figure 8's, reverse figure 8's, serpentines, hill work, backward hill work, counter arcs, circles, and lots and lots of long trotting.
Go back to the barrel pattern, SLOWLY! Don't rush your horse. Work on the basics again, then move up once you feel your horse is ready for the next step