Before you start your lesson know exactly what spot on the horse you want to move and where you want to move that spot.
For example, if you want to get your horse on the trailer, you only need to think about moving the left front foot forwards and backwards.
This breaks down to:
What (on the horse you want to move): Left front
Where (do you want it to move): Forwards and backwards
Why (is the horse going to move the foot): Tapping the hindquarter with the dressage whip
How (is the horse going to know he has done it correctly): Stop tapping (negative reinforcement) and praise the horse with a pat and verbal praise (positive reinforcement)
This becomes so much simpler and easier than trying to get the whole horse on to the trailer. If you can move the left front forwards and backwards then you can do that progressively moving towards the trailer and continue until the whole horse is on the trailer. Then you have taught your horse to load and unload quietly and safely.
Try to do this with everything you teach and remember if it isn't completely clear in your head (which foot where) then it is going to be impossible for you to get the horse to understand.
There is a free trailer loading video on the FREE STUFF page of this site. If you would like many many more examples of how to break the lesson down for your horse then join the Online Video Training Club and start training your horse today.