You know the importance of link building. but you don't know for sure search engines work, rank and give the authority rate of each website. I can promos that every thing you heard on this subject from SEOers are speculations. The only way for you to find out some of the truth about search engine ranking and good link building strategy is research. Get at least 5 keywords related to your website. Get the domains that ranks in the first 20 results for each search (100 domains) remove domains that have the exact search term on the domain now get a backlink checker tool and find out how these domain get links. try to get similar links from the same domains. It's hard but by going through results for 60-90 domains you can get great results. some domains are geting backlinks from forums, join those forums and get your backlinks some get from related blogs, from comments (comment on the same pages and more), from the blogroll (contact the webmaster to exchange links or to buy a link) directories, submit to the same directories, if there are a feature listing try to buy a feature listing too. if from articles, submit articles to the same directories.. and so on .. to get the maximum links you can, 60 domain research could take you a month or more but it worth it. remember to save all your results and research try it and see the results
i think it is good to check your competitors backlinks and place your links as well but you also need to be resourceful to make your rankings higher