Gone are the days when just any old link would improve your rankings. In 2008, you need to be extremely selective - quality rather than quantity.
Building links is one of the trickier parts of search engine optimisation and can make or break your campaign. The first thing to do is to find your linking opportunities.
There are 3 main ways of doing this:
1. Find all your competitors' links
Use Yahoo Site Explorer and find all the sites linking to your competitors, go through the list and filter out any low quality links (see below) and you have a viable list of link opportunities.
2. Search for your keywords in Google
If you search Google for your main keywords, most of the top results are likely to be from your competitors. Move down the list past the top 20 and you should find more varied results maybe from news sources etc. Try to alter your query to maybe only include pages from the last week or add a keyword such as blog, news or directory to your search.
Any page that ranks highly on Google is usually a very good place to get a link from so your list could be quite large. Narrow the list down by removing pages you know you can't get a link from.
3. Create new pages
The easiest way of doing this is to buy a hosted page on somebody else's site but this is against Google's guidelines, so is a risky tactic. Other methods include using something like Squidoo or a popular article directory, but these are not hugely effective.
The best method is to create something newsworthy on your website and hope that lots of news sites and blogs decide to write about it. This is called linkbaiting and can be quite tricky. Improve your chances of success by emailing bloggers to pitch your idea, using social news sites to promote your idea and even offering free products to people who write about you.
For example, if you published the results of a study saying that 89% of small business owners still didn't have a website you would release the study in an article on your site, send out a press release, pitch the idea to 50 leading bloggers in the web design & internet niche and then use social sites such as Digg and StumbleUpon to promote not only your own article but all the others that link to you.The value of a link
Once you have a list of places you might be able to get a link from, the next step is to decide which ones to pursue first.
Yahoo Site Explorer usually returns the links it thinks are most valuable at the top of the list, but this doesn't mean Google thinks the same.
To find out whether the links are going to help your Google rankings, I suggest examining the site and seeing if it looks like they publicly sell links. Any site that is obviously selling links risks having their link passing ability removed by Google.
At the very least, if you do get a link on the site, make sure your link isn't next to all the other paid ones - maybe buy or exchange a link in the middle of an article instead.
Next, look at a few pages of the site and see how well they rank on Google. Any site that ranks highly for its main keywords and lots of long tail terms is usually a trusted site and would be a great place for you to get a link from.
Finally, check the incoming links to both the site and the page your link could be placed on. Quality sites have quality backlinks and ideally the page you are wanting a link from should have a number of strong external backlinks too.