I know of a product that teaches how to use stumbleupon, but I'm not allowed to post the link here. It basically tells you how you should take some time to build up your reputation on the site, meet some friends, be active BEFORE you try to "thumbs up" your own site. But it has a lot more details into it. Anyhow, if you decided to use SU to drive traffic to your site, make SURE your site is a unique, interesting site that is worth visiting. When people use SU, they are expecting an unique site, NOT regaulr adsense, ecommerce, or sales page site. If you try to advertise those sites, not only will you not get good results, you'll have NEGATIVE impact due to users bad mouthing you and giving your horrible reviews.
Articles that suggest the kind of content that stumblers prefer versus regular users, techniques on how to increase your reputation and effect while stumbling. Basically, how to maximize your benefit from stumbleupon without resorting to dark-hat tactics like stumblexchange.
There's a good article about stumbleupon at http://www.squidoo.com/stumble-upon/ The sections about how SU works and how to get the most out of it are particularly useful. Riatsala