Here is a description from a farmer who had to take the test (even though his 80yo granny didn't):
The first part of the test involves a reversing manoeuvre. If you’ve had plenty of corn-cart experience this will seem pretty Mickey Mouse stuff. Just back yourself into a make-believe garage without hitting any cones or straying outside the lines.
Next is a 50-minute road route. Mine took in a motorway section, a one-way system and a few rural lanes. You’ll also have to pull over a couple of times and show that you can do a hill start without rolling, but it’s all run-of-the-mill stuff.
Once that’s done you just have to demonstrate that you are capable of coupling/uncoupling the trailer. It’s a simple case of remembering a routine.
The scoring is done just like a car test. That means you can amass up to 15 minors before you fail the test. However, commit one major fault and it’s game over.
I passed, but over the years I’ve seen several confident, competent friends fail the test, so it’s not as easy as it might seem. The pass rate for 2011/12 was 64.5%, which is up by almost 7% since 2008.
Think about the trailer you are going to use. In my experience, very short (luggage) trailers are the hardest. It helps a lot if you can see it in your mirrors too. Make sure that you have the correct mirrors properly adjusted. Make doubly sure that all the lights work, including reversing and fog if fitted. I take it that reversing round a corner into a parking space is no problem for you.