Links are an important part of SEO, but many people focus too much on them and not enough on what they can do on-site for SEO. There are some things which need to be done to websites on the site itself to really make Search Engine Optimization effective.
The first, and the biggest, is keywords. You know, of course, that you need to have keywords in your text so that search engines can figure out what your page is about and what search terms to rank it for. However, you also need keywords in places other than the text – like in links and headers. You don’t want to overuse headers, but have a good h1 header near the top of your page with some keywords in it is great for SEO. Also, you want your internal navigation to have keywords. If you use images or non-descriptive words, your internal navigation will have no SEO benefit and may even prevent search engines from indexing all parts of your site. However if your internal navigation consists of links with keywords about each page in them, the search engine will be able to crawl your entire site and will rank the subpages better.
Images are inherently bad for SEO. Search engines can’t tell if there’s text in an image, and they have no idea what an image is a picture of. Even if you have all your text in plain text and don’t put any in images, you will still want to use some pictures to make your site look better. When you do this, make sure to use alt and title attributes for your images so that search engines have something to index. Flash content is the same as images to search engines – they can’t read it. If you have to use Flash content, try to have some other text on the page for search engines to index.
Within your site, you main SEO goals revolve around 1) getting lots of keyword filled content (including text, links, and headers), and 2) getting search engines to find that content, by having a good navigation structure and using alt tags. There’s no way to guarantee what a search engine will or won’t see, and sometimes you have to adjust a design to get it noticed and ranked well. However making sure that you have readily available keywords for the search engines to find is your best bet for getting a good ranking.