Over on the Google Webmaster Central blog there is a post everybody with a web page should read. Titled "More guidance on building high-quality sites", Google lays out the kinds of questions they ask themselves and which they try to design their ranking algorithms to evaluate.
Regardless of how good or poor of a job Google’s ranking algorithms do of answering these questions today, they (and the other search engines) have a lot of very smart people working on this problem and they will only get better.
The more you start asking yourself questions like those listed instead of questions like "Do forum links help my rankings?" the better your pages will do. As an added bonus you (or your clients) will never have to fear another update like the recent Panda/Farmer update that hurt so many sites who had short term thinking.