It tough because they restrict you to a pretty small space for keywords. I stumbled into this one... but you should try using the names of competitive apps in your keywords, or perhaps complementary apps.
I un-intentionally did this once (one of our "competitors" had a fairly broad/generic app name), and it definitely seemed to kick start our downloads.
Not sure how often you plan on updating your app, but I'd definitely recommend experimenting with the keywords. Unfortunately you can only change them when pushing out an update, so you'd need to update frequently to do a lot of experimentation with them.