Link exchanges are probably the easiest way to boost your ranking on search engines. This involves posting a link to another company on your site in exchange for your link on their site.
Find merchants that sell complementary products and offer to trade text links or ads with them. If you're just starting out and your site doesn't get a lot of traffic, you may not get a one-to-one trade; be prepared to make concessions, at least until you have a track record — and traffic — to point to.