A good starting point is to check out your competitors backlinks using Yahoo Site explorer or alike, then visit the sites that link into them and see if they are from sources that you could obtain a backlink from.
Build backlinks from websites that relate to your industry, and use keyword rich anchor text if poss.
Remember: Quality, not quantity.
Also, use search engines and search for your industry accompanied by the words 'add link' or alike, for example if you were trying to build backlinks for a firm that sold computers you could Google 'computers add link'
That should get you started
Gem