The bit Spanner put up is a good guide - if you follow it step by step you should nail it. In a nutshell; set the piston to 2mm BTDC, adjust the points gap to 0.3-0.4mm by loosening the backplate screw (usually just above/right next to the contact breakers) and moving the plate. Do that screw up and slightly loosen the one at the other end of the points. If you've got a continuity meter, connect one probe to the grey or orange wire on the points depending which one you're doing and the other to a ground point. Otherwise, put your finest feeler gauge between the contact breakers (rizla/cigarette paper or something very thin will work). There's usually a v shape in the back plate near the loosened screw and a dink/hole behind it so you can use a screwdriver to lever/rotate the points around. Bring the points together slowly until the continuity goes to less than 4 Ohm. If you're using a rizla or feeler gauge, slide it about in the points gap while closing them until you feel the paper/gauge start to drag. You can tighten the screw now and rotate the crank to 2mm BTDC and check that everything is okey-dokey. Don't worry about the stuff about the 0.25mm card in that link - it's just describing cleaning the points. Edit: What Steve said.