Even if your gearing is still stock, the cheapest and most effective way to get more snap out of it is to gear it down a little. You can drop a tooth up front and not usually have to deal with chain length issues. If it's getting time to change the chain & sprockets, you can go up more teeth in the back, but this will require a longer chain if you're going 3 or more teeth.
As a general rule, a one tooth drop up front is approximately equal to a three tooth increase in the rear. Either one will make a noticable difference in how quick the bike is. The tradeoffs are increased rpm at cruise and usually a decrease in top speed.
(If the bike was geared too high from the factory - which is done sometimes to meet emissions or noise requirements by various governments - you can sometimes actually see an increase in top speed when you drop the gearing.)