Social Media: Twitter and Facebook
Adding an update which includes a link to a profile or product page etc is easy. The same works for Twitter, leaving a quick message and adding a link is really quick and easy. You can also use a tool like Tweet Adder to set up automated tweets throughout the day, so you are setting up multiple backlinks.

Social Bookmarking: Digg, Stumble and Tumble
Social bookmarking and blogging can be a very powerful tool because the search engine are always crawling them for new and popular content. I've found that Digg, Stumbleupon and Tumblr are great networks to submit to..

Posting on Forums
Find a forum that is relevant to your niche. Sign up and start making comments. Be careful not to spam, but leave helpful comments and answer questions, which can lead to sharing your link. Connecting with like minded business owners and people interested in your products can also lead to other activities like JVs. Usually a forum will allow you a link in your signature that people can click on to find out about you - ie generate traffic as well as back links

Comment on Blogs
Just as with forum posts, finding a high traffic blog will do the same. Leave a comment that is useful for the reader. Don't just write "great post", these won't get approved, write something useful and helpful!

An authority link is a backlink from a site already trusted by Google in terms of trust rank. It's a factor of Google Algorithm, in which once a web site is detected to be an authority, it will get more visibility in SERP's on related. You can began with Squidoo.com and HupPages.com, write on their page and spread your backlinks.

Link directories
whilst they might not be of a high quality, having links from an array of websites, with varying PRs and IP locations will actually make your backlinks profile look more natural and thus improving the whole profiles quality score.

When using link directories
1. Choose the best suited category when submit with them.

2. Don't mass submit your link to directories, avoid blacklisted by search engines.

3. Submit with relevant description and keywords but avoid over stuffing keywords.

If you are looking at how to get backlinks then from doing these things for 20 minutes a day you could easily get 15-20 backlinks every day, which would be over 5,000 in a year!

How to Get backlinks When You Don't Have The Time
You can outsource your link building to a reputable and affordable SEO company. There are many operators in India or the Philippines who will do the time intensive routines for you at very good rates. You can instruct your sub-contractor on the forums, blogs and pages you want backlinks from and they will do the work.