I just bought my raptor 350 about 3 weeks ago and i want to know what shoudl i do to get better performance with it but not spend alot of money

 

First thing i'd do is get new tires, at least the rears, because those stock ones are one of the biggest weaknesses on the entire machine. If you get some holeshots or razrs it'll be more stable, corner better, slide better, hook up better in all riding conditions, which all results in having more fun and going faster. The 2nd thing to do would be to replace the stock air filter with a clamp on k&n filter kit from pro design, noss, or gytr. The filter is easier to clean, and the clamp on eliminates the crappy stock design that can let dirt into your engine.

 

I agree, a clamp on filter is the cheapest and easiest way to free up a couple ponies IMO. If money is a big concern make that your first upgrade.
I put a UNI clamp on filter clamped straight on the back of the carb on my wifes predator. Its bone stock except that and it woke it up considerably. Keep in mind you will have to rejet the carb after doing that however. But carb jets are only $5 apiece.
Next upgrade should be an after market muffler. If you let more air in and more air out you will see a big difference.

 

if you are paying $5 for jets you are getting bent over the counter... they should be $2 max...