This should be your first stop.
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide
Next stop should be a guide for your particular motherboard. Google is your friend.
You should be able to reach 3.0 GHz with the stock cooler. You should be able to reach 3.3 GHz almost any good cooled. Anything more than that will take serious cooling.
Do not exceed 1.5 volts core voltage and keep your load temps under 70 C.