Working on an overdrive pedal, here’s a few resources about clipping and distortion:

• http://blackstoneappliances.com/dist101.html
• http://www.geofex.com/effxfaq/distn101.htm
• http://www.diystompboxes.com/wiki/index.php?title=Simple_mods

And a more general resource about the TubeScreamer circuit:

• http://www.electrosmash.com/tube-screamer-analysis

And a good compilation of general breadboard techniques:

• http://m8051.blogspot.com/2011/09/bread-board-tips-and-tricks-beginner-to.html