Now to overclock follow these steps.
1. Start with default settings.
2. Increase core clock by 10 or 15.
3. Stress test it to make sure its stable.
4. Repeat steps 2 and 3 until your GPU crashes.
5. Once you know where it crashes bring the core clock down 10 or 15.
6. Do the same with the memory clock.
Always watch the temperature... if it gets too high, increase your fan speed.
Also if you want to get a higher OC you can increase the cards voltage, but only do this if you know what your are doing as it can damage or destroy your card.
One last thing, always remember if it crashes, it cant handle the OC you have... just dial it back if this happens.