What type of ridng do you do......and how do you like the power delivery of your bike now?
Basically, if you want faster acceleration but less top speed (mx,tight woods riding) then you need to increase the size of you rear sprocket or decrease the size of the front sprocket. For more speed (open riding areas usually)decrease the rear sprocket size.
Most go up or down 2 teeth on the rear sprocket to get the desired effect. If you choose to change the front sprocket, remember that a 1 tooth change is equal to changing 4 teeth on rear sprocket. This may be a bit drastic of a change though.
I ride mostly tight woods with various types of terrain. I think faster acceleration would help me out a little bit. The power is pretty good but I think I might try a rear sprocket that is 2 teeth bigger. Thanks