It's not so easy to explain the whole SEO process in a comment. People wrote books for that. A good starting point is guides by seomoz.org. Blog comments, paid

It's not so easy to explain the whole SEO process in a comment. People wrote books for that. A good starting point is guides by seomoz.org. Blog comments, paid links are not recommended, from comments no link juice passes, and google already announced that the sites having paid links will be penalized. Reciprocal links are also not recommended, from homepage to homepage link exchange can be harmful, google spam team everyday reviews websites with that issue. Best way for the backlinks is having valuable content that people will link back without asking them.