In today's scenario while Google doing a lots of changes in it's algorithm, Your website needs strong link juice for ranking high in Google or any search engine. As an SEO consultant i realize in my life the importance of link juice to our website but that should be done in a right way.
So here i will explain what fields we should avoid and what we consider while doing link building for our website.

The factors that should be avoid while taking a link on your site:

1. Avoid No follow links as these links never crawled by Google bot.
2. Avoid links from those websites which has already a number of links on it's pages. or a link farm.
3. Avoid links from porn, Gamble sites. Google consider bad links coming from these sites.
4. Always avoid irrelevant topic/theme while taking links.
5. Avoid Bad neighbor links. Leave the pages which have bad links like porn or casino related links.
6. Avoid links from websites which has 0 or no page rank.
7. Avoid links from those websites which has never crawled/cache by Google crawler.
8. Never use paid links. Google hate these links.
9. Avoid excessive links.
10. Avoid repeated links from same website or same IP address.
11. Avoid taking links from duplicate or bad quality content.
12. Avoid low quality directory or bookmarking sites.
13. Avoid links from sites where you find widely distributed links in the footers or templates of various sites.
14. Don't use too many links from a single page (overly optimized) content. For example: There are many wedding rings on the market. If you want to have a wedding, you will have to pick the best ring. You will also need to buy flowers and a wedding dress.

Link Building factors that should be Consider:

1. Use do follow links.
2. Always try to take contextual links (Links within the content). You can take links from third party blogs, forums, Article,  Press releases and etc.
3. Try to take links from the websites which has high Google page rank.
4. Always follow Google link building parameters.
5. Always take links from fresh or unique content.
6. Always use natural links.

Always remember Google never hate link building but dislikes bad quality links which has earn by unethical things or the links which don't follow Google link building guidelines.

What Matt Cutts syas about nofollow links?

What Woorank Expert says about link building?