Always post ten community engaged links between each self-promotional piece you pin or stumble.
It is that easy!
Find photos you love, products you'd like to buy, or fun projects, and pin/stumble them. If all you do is post from your own site, you will fail to gain followers on Pinterest and will not have posts picked up by StumpleUpon. (Tip: With StumbleUpon, make sure you are placing a quick description in the comment section of each post.)
After every ten pins/stumbles, post something from your site and watch your numbers grow!