Slider advice

I’m going to try to add another pitch to my arsenal before next season starts. Right now I throw a fastball and changeup, and I want to add a slider. I’ve tried several different grips and deliveries, but I can’t seem to get the results I want.
Does anyone have any advice on how to throw an effective slider or do you know of any sites where I can find good information about throwing the slider?

http://stevecarlton.com/pages/slider.html

nobody ever threw a better one so i think thats a good place to start.