My warmup (although I don't jump) involves at least 10 minutes of walking on a long rein, asking the horse to come in front of my leg and stretch into a big marching walk. From that, I will start to bring the horse up into a contact, do some leg yield, walk-halt-walk transitions and serpentines before I start trotting. Then same thing in trot, leg yield, transitions and serpentines. A little bit of shoulder in and then into canter, some leg yield and transitions in canter. A 5 minute long rein walk and then into the serious work.
I know when my horse is warmed up sufficiently in body AND mind when he is working ahead of my leg, is responsive to my aids, is over the back and working consistently into a contact.
Just remember that a warm up is not just about 'warming up' their body. You also need to warm up their mind in preparation for the tougher work to follow, so make sure they're really tuned into your aids before you start your harder work.