I did the FAA IR just after passing my FI test and found it to be quite hard work.
Then I insructed for about 250 hrs before doing the JAR IR conversion.
The test for JAA IR was actually quite easy, relative to what I was expecting that is.
To be fair, the test ran almost exactlyl as briefed on the ground which helped.
The instructing helped me in the following ways.
1. Using the radio everyday at work.
2. Flying accurate attitudes. This allowed me to instruct and chat to students, talk on the radio and still demonstrate that flying can be done to precise tolerances.
3. When your own students go for test, you realise that they have all the skills necessary. The test is just a quality control exercise by the CAA to check this.
I think the last one is the most important. If you are going to fly for a living just accept that tests are a part of life. You will do well in some, crap in others, but you will pass at some point.
Good luck anyway.
FIS