Pull requests are awesome, and I'd love to see more of them on this project.
Create a fork, clone, submit pull request! I'll try to review things as quickly as possible!
I try to follow the the Haskell Style Guideline. Code should compile cleanly with no warnings with -Wall and cleanly pass the hlint (see http://community.haskell.org/~ndm/hlint/) inspections with no suggestions. Everything file should cleanly pass scan (see http://projects.haskell.org/style-scanner/).
If you want to change/add major new functionality, then create an issue to discuss your idea and let's talk about it before you start to make sure it fits with any plans or open branches.