Generally speaking, the quality of the traffic you get from StumbeUpon can be fairly poor.
Users hit the 'Stumble' button on their toolbar and it will physically take you to a random site that fits within your varying pre-selected interests.
It doesn't give you a selection of sites to choose from.
You are just taken to a random website with no idea of where it's taking you until you are there.
And it's quite often disappointing once you do get there.
Put yourself in the Stumblers shoes.
If you've just landed on a website that you don't like or that doesn't look interesting or engaging you'll just hit the Stumble button again and see where else you land until you find something that draws you in.
Keeping that in mind, you need to do what you can to keep these visitors sticking around longer - you need to take steps to ensure your website engages with as many visitors as possible.
Some of the basic areas you should be looking at are: Design Does this look appealing? Does it draw people in and make them want to look deeper? Sometimes a basic design with a well placed image is adequate and leaves plenty of room for good content.
URL Is this easy to remember? Are people likely to bring it up in conversation and tell their friends or contacts? Adverts Don't make your website look too untidy with numerous adverts.
You don't want your visitors first impressions to be that your website is all about making money and nothing else.
Content Does your website contain good content? Is it compelling, informative, useful or interesting? Is it updated regularly? Is there enough of it to bring people back if it is something that interests them? These are just some of the areas you can look at to help increase the amount of time not only stumblers stay on your site but any visitor.
It's likely that people that intentionally visit your website will stay around a little longer than those that have Stumbled you but by applying some of the above ideas will help bring them back time and time again and help encourage them to stay around longer.