Stock....the ttr 230 is shitty, but here are a few cheap ways too make it a deccent off-road bike. These are good mods to do if you like the size and that stuff but would like a bit more bite.
1.) Remove the exhaust insert. This will allow the bike to accelerate faster. Without it there will only still be a spark arrestor which keeps it legal. Also....if you do this, don't be a retard and rev it up in places where u gunna get into shit for it.
2.) Remove the snorkel from the top of the airbox. This will give the bike more overall power. This can be doon by breaking the seal using a knife and a small flat head screw driver, and prying it out with a larger flat head screwdriver. After, drill 3-4 quarter inch holes on top of the airbox, but make sure they are above the half of the box with the filter...duh!
Note: it will still shed pretty good but make sure to check/clean the filter more often
3.) Purchase and aftermarket, high air flow filter, such as a twin-air filter. They run between 25-40 bucks. If your more into riding in pitts and dry areas u might want to consider removing the airbox and buying a universal mount with a K&N paper element filter. If you do so, the bike must be re-jetted and the filter must be cleaned regualry, pretty much after every ride.
4.) Adjust the susspension to what you like....if you plan to do any kind of jump with this bike, ur going to have to realing tighten up the shocks obviously.
5.) Last of all purchase items such as handgaurds and crapp like that if u want...
With those mods you will have well increased acceration and power and a bike that will max around 69-72 m.p.h depending on the conditons. But if your looking for speed, air, and power your better off just buying a different bike.