mstr-of-ppts get yourself down to your local newsagents and buy a copy of the newest issue of the total guitar mag (its got dimebag darrell on the cover), there is a lesson in it teaching some basic wah techniques like accents, percussive strums, etc and then there's a tiny section of a blues solo to try out the techniques on.

That should get you started mate, best thing to do with a wah pedal though is to mess around really. Doesnt hurt to try some excersises like in total guitar though, as that will give you an idea about some of the sounds you can get out of it and how to get them.