Linking with quality partners is one way of practicing SEO as it can help boost your rankings in the search engines. Link popularity is a factor that many search engines use when ranking web pages within their indexes. Nineteen of the top twenty search engines currently look for this when ranking sites for their search engine pages.
Whine it comes to linking, quantity has been important in the past but the recent trend is for the search engine to consider the quality of the links. The most expedient way to get expedient links is to link yourself to popular directories such as the Open Directory Project, which is considered high quality because it is edited by humans and not search engine spiders. Once Google and Lycos sees you listed in this site they usually add you and boost your ranking.
It also hopes to look for partners whose products or services have something to do with what you are selling. For instance if you have a site selling search engine optimization software you might want to link up with a site selling an easy ezine or article submitter as the two products compliment each either. However the important thing is to choose a partner that is not going to imitate you or grow into selling the same products that you are.
When you look for such sites look for quality, highly ranked, non-competing sites that have plenty of working links or resource pages. Even better, many of the links on their pages may be a valuable resource when it comes to finding links that also suit your site.
The best way to ask for a link from a big site is to add their link first to show that you intend to work with them in good faith and then ask them if they would like to trade links with you. You can always remove it if they decide to be nasty and say no which is more common than ever with some of the larger sites.