Hm, Greebling refers to the tiny-winy details that make stuff look technical…there are a few possibilities how to actually do it.
First, the automatic way using a script (the original script called Greeble was for 3DSM, as far as I know). In Blender you have the Discombombulator script which provides nice results but is somewhat limited.
The, in my opinion, far better way to achieve really good looking results is to do it manually. Of course, this also takes a lot of time but it is worth it. Look at reference pictures (especially from Star Wars) and tutorials to see how you can do it; some places to start might be these ones:
Personally, I always loved to do that kind of stuff ;D