Try and minimize the cost involved purely in learning to interpret the instruments. By this, I mean try and spend as much time as you can on the Sim (or even FS2002 or whatever) just getting your head around what the instruments are telling you in an NDB hold, for example. Learn how to calculate drift allowance when airborne, not by using the whiz wheel on the ground before you go, and get to the point where you don't have to tilt your head on one side to work out which hold entry you are going to fly!
All of this is bread and butter stuff which would be far better to have clear in your head before you start blasting around ina twin at £300 per hour or whatever!
Further than that, enjoy! It is in fact easier flying IFR in CAS than VFR outside. No need to lookout or keep clear of this or that bit of airspace, and you are spoon-fed from one controller to the next all the way back to the apron!