I think the answer you are after (as your question is very vague) is start with Google Adsense it is easy to set up and generally performs very well. Then test the different ad placemetns and layouts until you find a good combination.
Then test other Networks until you find what works best for you
And that's all there is too it....
Except then you need to develop your own products or learn CPA..
Then you have to learn... then you have to learn...
