I don't do join up often. Sometimes with the horses I help break. Here's how I learned:
Its just like lunging, just with more interaction. Its to be done in a round pen. Warm the horse up, increasing the speed as you go. If your horse is paying attention, there nose will be slightly tilted. When your horse's ears are moving all around, and the inside ear is constantly toward you, you horse is letting you know they are following. When your horse begins licking its lips and chewing...they are asking to stop. Allow them to stop. Turn away from them and just stand there for a few seconds. Then begin walking slowly away from the horse. If the join up is a success, the horse with begin to follow you...want to be with you.
Its all about body language, bonding, and getting to know one another in my opinion. Please, anyone let me know how I've explained this...
And take a look at these pics if it helps at all!
See how she simply walks away and the horse yearns for her attention, basically
I say this is cheating. Don't coax your horse, let them WANT to be with you.
To me, a nice example...
Sorry I couldn't find any good pics but I hope this helps!