One of the best ways to reduce bounce rate is to make people stay on your website. As obvious, curiosity of what's in it is the best way to do it. Someone came to your website, landed on some page ( preferably home page ). A lot of listing is given in forums and blogs. ie, sidebar contents like popular posts, new posts, recent posts, recent comments etc. By using sidebar ( which are available on all pages ) is the best way to take user attention to highlighted content.
If you want to kill / reduce bounce rate, another option is to use pop up blocks. It can be either an offer ( which is interesting ), a freebie or something that would keep the user on your webpage till Google says he has not bounced off immediately.
A good theme, readable and enjoyable may do both good and bad. Bad, when you are not strong content-wise. The good thing about a good style for your website with a cool colour scheme is that people make actually be interesting in looking what all things are available on your website. This will in effect keep the browsing time high and user won't be ranked as bounced off