In short: your content should be visible and accessible to bots. If you start a page with banners and other graphic material, use proper alt tags. It is also a good practice to have few lines of text before ads jump in. Java can be a problem as well. Flash is even worse. Old plain http, healthy linking structure (internal and external), fast loading speed (not too long articles, not too huge pictures), reasonable amount of h1, h2 and other tags, ... - this are the key ingredients to success.
Hope this helps.