The best way to overclock is done manually. If you are new to overclocking with video cards, I would suggest telling us the kind of card you have and we can then tell you a few things or link guides that specify how to overclock your particular card.
If you are new to overclocking in all aspects--CPU, RAM, GPU's, etc.--then this is just a general introduction to it.
Click
Like the video cards, the type of hardware you have will determine the method in which you use to overclock, but there are basic principles that apply universally.
(i.e. Voltages, Heat, Frequency increase intervals, etc.)
What's your build?