Crosswind,
You seem to have the right approach because you are thinking about the IR before you have started spending the money.
First thing is to get the standards document from the nice people at the CAA. Believe it or not it is available free-of-charge from Flight Crew Licensing. (Or it was 18 months ago when I did my IR training) . The document has an easily remembered catchy title:
"Standards Document 1 Version 2 - Notes for the guidance of applicants taking the initial instrument rating flight test (Aeroplanes)." This tells you everything you want to know about the test and what will and won't fail you.
Next thing, while you are waiting for the postman to deliver the above (unless its now on their internet site), is to ring up your selected training establishment and get the CAA approved checklist for the aircraft you will be using faxed over to you. Read it all, but learn absolutely perfectly all the checks that have to be performed from memory. These will start with the after take-off items. Spend as long as you like learning these, you're not spendiing five quid per minute at this stage, but get them burned firmly into your brain so you can rattle them off at any time, in any circumstances, with any distractions.
Another tip, if a list seems to have too many items to memorise, group them into threes and learn them as groups of three. E.g. for after t/o:
BUF: Brakes (stop wheels spinning)
Undercarriage
Flaps
PTL: Power (set climb power)
T (Ts & Ps)
L (Landing light off)
You don't want to be doing anything at five quid per minute in the aircraft that you can learn on the ground.
As soon as I completed the training and got the pass, I wrote myself a complete set of notes to remind me of everything to remember / not get wrong, from the planning to the landing. Studying this before the renewal made the renewal a breeze.
I keep adding to it and after the renewal its now reached over a dozen pages. It also acts as a reference so I don't start letting my standards slip.
Another thing you can do for free before starting the flying is to revise your Aerad / Jepp approach plates and en-route charts. You really have to be up-to-speed on the route planning and be able to do it accurately under (time) pressure.
Finally, Good Luck !