I can give a few tips @mumsiedarlingrevolta - there are quite a few blogs and websites to be found - although the producers like to be fairly secretive about the process.
Without giving away trade secrets, here goes. These shows get around 60,000 applications so you must stand out in some way. How do you do that? God knows - but if you're good at filling in forms for a job you've a head start. They like confident people who are fairly knowledgeable and likeable. Stoic types need not apply - it doesn't come across well on screen. It's a bit like a job application, but more fun. Trying to impress starts when you press Enter so make an effort to impress right there.
Be a bigger version of yourself - without fibbing or looking silly. If you say that you're adventurous then sound that way if they ring you back, again stoic doesn't hack it. Sound enthusiastic and confident, delighted at the prospect of appearing. Carry this through if you get an audition.
At audition you must introduce yourself on camera (for about 2 minutes) so practice this aloud at home, something along the lines of "My name is Freda Bloggs, I'm 35 and work as a funeral celebrant. My hobbies are flower arranging, wild swimming and knitting hats for neonatal babies. My favourite Chaser is ..... because ..... and if I win anything I'd spend the money on a sports car" or whatever. If you try this at home it'll feel like second nature - eventually .
However, life isn't fair and even if you get all that right you still might not be picked - but at least you tried and gave it all you've got. And of course it's true, being in the studio isn't the same of watching it on telly - you might pass on a question instead of guessing because you're scared of looking silly. Regard it as a fun day out, even if all you take home is a memory - hopefully a good one.