1. Submit your post first - this removes the 2 step submission process for your readers making sharing easier.
2. Use the Su.Pr Link Shortener - this is golden, I've more than tripled my stumbleupon traffic by doing this. Instead of using other link shorteners to share your content using Su.Pr.
Not only can you forward the content to other social sites, but you also automatically send those who click the link to the SU version of the page with the toolbar.
When (if) they like your page it helps snowball more traffic to the page via Stumbleupon.