Good question! In my opinion, A/B and multivariate tests are a good way to increase bounce rates. Often, adding a few images, adding bullet points, breaking up your text in smaller paragraphs can help decrease bounce rate.
What you should keep in mind, though, is that different kind of traffic tends to have different bounce rates. So facebook, twitter, digg, stumbleupon ... normally have quite high bounce rates. The same goes for RSS feeds: if people suscribe to your blog, often they will come to your page just to read the one article, without browsing your site. It can therefore help to include links to other parts of your sites, related blog posts, and with a call to action in your blog post.
For reducing bounce rates of Google (or other search engine) organic traffic, you should aim for page titles that relate to the content of the page. When someone clicks on a search result, they will at least have read the title. Now if your h1 is very different from that, chances are, people will leave your site right away, assuming it does not offer what they are looking for.
The same goes for PPC. Make sure your ad copy matches the landing page. In order to achieve this, split your keywords in different ad groups, according to the topic. Then tailor the ads towards the keywords and the landing page. PPC also allows you to run a lot of experiments, so take advantage of this and apply what you learn from it to other areas.