This methodology will be work for increase digg followers Keep your self Active: Keep yourself active so that others can see you active and people mostly love to follow active people, as there is no benefit to talk with dead things.
Ask your friends in other network to Follow you: To get more followers ask people coming on your site to follow you on Digg and tell people at social networks to join you at Digg.
Follow Others: Try to follow other fellow bloggers it will generate good relations and they will soon follow you back and realize your importance.
Take Part In conversations: Take part in active conversations going on, and give very proper and reasonable answer to them so that people will take interest in you, and try to know more about you.
Taking Part in other people Submissions: You must take part in other people submissions so that people will like you more.
For Stumble:
Post Interesting topics
Join/ Invite your friends by mail
Give Regular Update
Join conversation
and similar activity
As the first responder said for the most part you just have to network with people and the rest will take care of itself.
You can also of course submit other bookmarks pointing to your diff and stumbleupon submissions and even use other forms of linking to link to your bookmarks if you really want to increase the traffic from thesetwo specified sites.
Not a matter about digg or stumbleupon but for all social media sites,there is need to be active.Try to increase your followers and always like other people stories.Also one more important thing and that is very high quality content.If you ll share quality and relevant content to your community then there might be chances to get huge traffic from these websites.
It will be difficult in increasing followers in stumbleupon, because of the low user interface. But digg should be pretty easy. I have always seen an increase of couple of followers whenever i post a new link. Its sitting pretty well at around 400.
You have to really build your friend base first. You also have to be very active and support your friends so they will want to support you. It does take a while so don’t think you can build it up quickly.