Well I used to use an automated software called bookmarking demon for links but left it. It's kinda spam tool so won;t recommend it to anyone - I would rather recommend a power user at those sites and do your promotion i perfectly whitehat way .
1. Observe. Choose your preferred social bookmarking site and particular niche, then subscribe to it. The more specific the category, the better. Get a feel for the trends. Know what works and what doesn’t.
2. Keep ahead. Also, subscribe to the top blogs or sites related to your niche. Your RSS reader should have at least 20 of those. Some of these are probably among the most dugg sites already.
3. Branding. Join the site using a short catchy username, and an equally memorable avatar.
4. Get personal. Go to the Upcoming section and try to digg the ones you think will make it to the top. More importantly, be the first one to add comment of support. Add them as friend and check their profiles constantly to digg their other submissions. If you do this, they’ll most likely return the favor.
5. Test. Once you’ve accumulated about 50 friends or so, start digging posts from your own blog, one at a time. Don’t spam or you’ll get banned.