There's no real secret to it, its a bit of an old chestnut but keep your eyes open and mouth shut. There is alot to take in and you will always get those on the course that have been retained and think they know everything, well they dont. (no offence to the majority of retained)
There is a lot of theory to take in and some of it is mind numbingly boring! As for fitness, well you'll be running around alot in fire kit hose running and the like so it pays to stay in shape. Each brigade/training centre runs their courses differently but they all have to meet the home office standards. Ladders, hoses, pumps (alot of theory as well as practical), hydraulics (zzzzz) and not just the cutting and spreading type! Breathing apparatus which for those totaly new to it can be a daunting experience but vital in todays service and very enjoyable. There are also the interesting delights of building construction theory not to mention all of the new dimension and water safety stuff!
My advice is turn up and enjoy, its a fantastic career & job if you can ignore all of the side issues such as rank to role and IRMP (well for the moment at least). O and don't be put off by the course winger as every course has one!
Good Luck hope it helps a bit.