Lee,

What do you need to know?

First thing to bear in mind is the expense. Whilst the track day itself might be cheap, the extra costs can soon add up. A track day will be around the £100 minimum (usually), and then add costs for fuel on the day, and travelling there and back, and count int cost of rapid wear on brakes and tyres.

Most track days I'd budget a minimum of £200 (bare minimum)........

Little more specific info you're after?