Link building is the heart of SEO. Without link building you cannot rank in higher search results.
Yes, i agree with cuinee. Those are the most preferred link building methods you have to use in your campaign. But there should be some ratio while building such links.
4-5 Home page links per month ( I Prefer theme related links)
20 Contextual links from where you should have to drive min traffic to your site.
Like wise, you have to maintain some ratio while building links. I know, these are the things which can be done by only professionals.
Well, we have been using Link-building-service.info 's link building services for our company. Honestly,they are doing good job. I prefer you to use their services for your link building campaign. They will track your serps from beginning.