My first tip is one I only recently discovered: use a thesaurus. I don't know what it was; maybe I was afraid to use it, like it's admitting that I don't know everything, or maybe I just didn't realize how helpful they were. But as soon as I conceded and started using a thesaurus whenever I felt that my word choice wasn't flowing properly, I found that my writing became a lot more satisfying to read.
My second tip is less clear-cut, and is probably not for everyone. Read some postmodern authors like Pynchon or Nabokov, masters of really varied writing. If you already have, do it again. See what they do to make their writing stand apart. Try to write like that. It's going to be a very poor simulation, but eventually you'll incorporate the bits that you like into your own style.