I did it (RCB) t'other week, (passed!)...advice I'd pass on:
Maths: Mine is shocking, but I managed... learn the 6 times table as a priority (6 keeps cropping up)...others just basic knowledge....all the maths questions are simple as long as you think straight (i.e. 30 miles, 3mph etc!!! - remember someone on my briefing back in November got so worked up he couldn't think of 10 miles at 10 mph! - so stay calm!)
Group discussion CONTRIBUTE. they are not terribly interested in your ideas as long as they arn't absurd...just say something...
Leader command tasks...EXPLAIN the plan, and don't be scared to take advice... leaderless CONTRIBUTE but don't keep pressingh your idea at the expense of other peoples...you may see it as brilliant, but it may not be.
Interviews - absolute doddle
Planning ex - there is space for 5 or so plans SO FILL IT UP!! even if 3 of them are slight variations of each other (mine were), even if are blingingly obviously crap, it shows you have considered options and deduced the best on.
When quizzed about the planning ex, don't go changing your plan every 3 seconds when something comes to light that you've missed, just say 'ah...missed that' rather than stumbling on pretending you hadn't missed it. (digging out of hole et al..)
read a decent broadsheet every day (torygraph is good!), and you'll be sorted.
Seem to remember the World's Fattest PO who was trying for an Army Cadet Commission on my TCB, and a guy who was a Barrister, HAC and whose Father was big style Army. Very nice bloke, but no way was he ever going to fail
In other words, relax and accept the outcome largely as an issue of fate, before you start. If you do, you are more likely to enjoy the experience. If you do that, you will appear at the most relaxed, happy and capable you can be, and your performance will reflect this!
These sage words were given to me and many other officers who were all successful. In turn, I passed them on to many soldiers who were subsequently commissioned.
You're given 3 minutes to tackle the Main RCB obstacle course. You have to complete each obstacle properly, then use the remaining time to attempt as many others as possible. Once you've done one lap, you can repeat the same obstacle for the remainder of the 3 mins. It did seem a very lond 3 mins though.