You are reading this article and it proves that there is no need to explain the need and importance of Link Building in SEO and for better PR (Page Rank).
I assume that you are already aware of the SEO, PR (Page Rank) and BackLink building.
Here I am going to discuss top 5 mistakes that most people do when they are newbie to SEO field.
I will explain which these mistakes are, why they should be avoided and how they harm your SEO efforts.
If you are thinking to hire an SEO services, I strongly recommend you to go through this article and your SEO or package, to find out any possible use of one of the below link building mistake.
Before I explain each link building mistake that we usually do, in details, here is a quick overview.

1. BackLink from non relevant pages.
   
2. BackLink from spam, duplicated, or suspicious pages.
   
3. Linking from lower valuable pages than yours.
   
4. Linking with wrong anchor keyword or without anchor link.
   
5. Speed of the link building campaign.
   

So, let us start digging each mistake listed above in details.

1. BackLink from non relevant pages.
   Getting a vote from totally non relevant pages would not much impact on your Google PR (Page Rank).
   If your blog or web page is about "Web development", you should get BackLinks from the pages in the same field or niche of web development.
   Links from similar pages will affect a lot to your SEO.
   
2. Back link from spam, duplicated, or suspicious pages.
   Back link to your page must be from valuable page.
   If linking page is not original and informative, it's link to your page will be surely a waste of time.
   Do not waste time in building links from duplicate, spam or not so informative pages.
   
3. Linking from lower valuable pages than yours.
   Always, remember the purpose of back link, it's for improving your Google PR (Page Rank) and hence getting links from lower ranking pages than PR (Page Rank) of your page will really not make enough sense that should be given your valuable time.
   
4. Linking with wrong anchor keyword or without anchor link.
   Do not forget to use anchor link on your main keyword of linked page while building backlink.
   It doubles the value of backlinks and also helps your improve your SERP (Search Engine Result Pages) ranking.
   
5. Speed of the link building campaign.
   Always work naturally.
   Suppose your site is older than a year and already indexed all pages in Google, than getting few hundred backlinks through your link building comparing will not harm your SEO credibility, but suppose your site is new and just a few days of age, than getting fast backlinks will really alarm your SEO credibility and would look like very suspicious in eyes of Google.
   So work slowly and smartly.
   

Hope these 5 Link Building Mistakes help you avoid and harm you may create to your site by mistake.
More best SEO strategies will be discussed in my next articles.