From my experience as an ex-show jumper turned eventer, I find trot sets to be the best and easiest way to get a horse fit. For a horse coming back from a month long vacation, I start with 30 min walk followed by 1*5 min and add 1 min every day until the horse is trotting 30 min in 5 min sets with 2-3 min breaks in between sets. I then start regular flatwork and jumping. If I need a fitter, event ready horse, I will add 4 min canter sets (at 400-450 m/m), building up until the horse is doing 3 sets with 5 min breaks in between. I usually keep it to that for a horse competing at the national CI*(courses between 5 and 6 min generally at 525 m/m). I plan so the horse has 4 "full" workouts (3 canter sets) before the event, last one 4 days before the show. Hope that helps!