Sorry but this is too generic as a question: there are books and online courses about SEO, you may want to start from there. This forum can only help you with specific issues. For example, one such detailed question would look like this: "The webpage on http://mydomain has really a lower page rank since I changed the layout. It used to look like A.png. What are the possible causes for such change in ranking?"
Edit your message to be more specific please.