In the far-flung future, Earthmen have been subjugated by a technically advanced, but culturally backward, alien race. Through playing on the aliens' superstitions--and their unexpected coffee addictions--humans begin to get the upper hand again in John Brunner's light, tight space opera The Super Barbarians.
Brunner was a hugely prolific and popular sci-fi author in the 60s and 70s, but I find his writing kind of mixed and have picked up and put down a lot of his books over the years. I stuck with this one because it didn't take itself too seriously and had a brisk, tidy plot.
This one caught my fancy after seeing it on a flea market goodbye shelf and I read it at a good pace. I continue to keep a lookout for John Brunner's work.