This is actually a topic I know a little about... What you do to the bike depends on what class, and what series you want to race it in. Take a look at the rules for the series, and build the bike to suit.
I would say for the first year-- don't get silly with building the bike, and race the Stock Mod class. You won't get the money back if you decide to sell the bike later. I'd start with a 4th gear shift drum, 2008 + output shaft, pipe, cam, 85/40 jetting, 14-15/37 gearing, tapered steering bearings, Pivot Works swingarm bearings, bars, +1' shifter, tires WITH a rear rim lock, and do something with the suspension. Call Odi at Feal to help you with a CORRECT setup for your weight. That will be the best money spent. Fox Float Shock is great. Also-- pull out the foot peg bolts, and take them to your local hardware store to match them up with some longer ones, or you will rip the stock bolts out of the cases the first time you get any big air on the bike. Install them with blue loctite and check them regularly for tightness.
Check out Planet Minis, and you'll see a ton of 110 builds in various states of tune. IMO-- you can spend $10K on a pit bike, but you'll never have more fun than mobbing a stocker 110 with your buds just for fun. Hope this helps, and hope to see ya at the track. Also-- check out the Apple Cabin pit bike track. It's the most fun of any pit bike track I've ridden. --Tony C.