Originally Posted by Adriaan
I suggest the following. Get something in the front that you can always use, the high 40s is your best bet if your not used to riding a track and skidding. Otherwise you can move into the low 50s, a 50 or 52 is a great front crank.
The rear is what can keep changing. Depending entirely on the power of your legs, I would suggest something around 15 to 17. If you have powerful legs, then a 13 or 14 may be more your style, but it becomes harder to skid and stop if you pair it up with a large enough front crank.
My 2 cents.
Any of those suggestions will result in huge gears, except for the 17 cog. Try to stick to low 80's to mid 70's as far as the gear inches go. A gear in this range will allow you to spin, give you enough speed, enough of a jump for acceleration, and still allow you decent leverage to stop.