First, is this a wet kit or dry kit. What I mean by dont lean it out, is, install it according to the directions. They will tell you which jets to use together(if its a wet kit), dont change these around. You should use a WOT activation switch(the nitrous only comes on at wide open throttle). If your timing is currently advanced to max without pinging, then you may need to reduce timing by 2* for each 50hp in spray, but test this by driving the car and listening for spark knock. Best way to control timing with nitrous is with a aftermarket(MSD or other) ignition box with timing retard function. This way you can have full timing while in normal driving,and when you switch on the nitrous the timing will automatically retard the amount you program it to, so you dont have to keep popping you hood to move your distributor.
Heres a spark plug guide.
http://www.buckeye-illinois.com/sparkplugs.htm