I did my CRI course at Andrewsfield last year. At the time I only had 350 hours total time so I was a bit worried about what the course would be like and whether I would be up to it. I only have a bog standard PPL. I revised almost the entire PPL syllabus before starting the course and Andrewsfield sent me a list comprising about 200 questions that I went through before starting the course. All of this proved very worthwhile. If you just roll up without having good theoretical knowledge and knowledge of the ANO etc. then you really will struggle to do well.
My day started at 8am, swatting up or writing briefings, followed by a full day of study and flying at the airfield then more study and perfecting my briefings till 10pm.
You get thrown in at the deep end at Andrewsfield. Within a couple of hours of arriving there I was standing in front of an instructor giving a pre-flight briefing on stalls. At the end of 5 days you'll be expected to have produced good short briefings on circuits, PFLs, stalls, circuits etc. plus a long (45 minute) brief on a topic decided by the examiner. My long brief was tailwheel conversions. Your briefings will be scrutinised and picked apart, line by line!
The test itself, from start to finish, was over 4 hours long. This included giving a pre-flight briefing, the flight itself, a long brief and general questioning. Carol Cooper was my examiner. I wasn't perfect (who is?) but being told I'd passed the course was a great feeling.
Other good ideas:- I hadn't flown a Cessna 152 for 3 years or so before doing the course. I wish I'd spent a couple of hours with an FI in one before starting the course. A few hours in the RHS with an FI would have helped as well, though to be honest, flying from the right seat didn't really cause me any problems, possibly because my my own aeroplane is flown with throttle in left hand and stick in right hand.
Although, ultimately, your knowledge and skills will get you through the test, arriving at your chosen flight school with enthusiasm, a positive attitude and good theoretical knowledge will go a long way in helping you to achieve the CRI rating.
I really enjoy instructing and hope to have an FI rating within a couple of years.