If you’re interested in learning Clojure, there’s an opportunity coming up. I’m teaching an introductory Clojure class in Kansas City. It starts in early January and will last for four weeks, meeting twice a week on Tuesday and Thursday evening.
Picking the right data structure makes a big difference to your code. If like me you're coming from a language with fewer data structures (or at least where using generic data structures instead of custom classes is not the norm), then it's easy to follow habit and model data the way you're used to. Don't be afraid to use Clojure's data structures! Here's an example where I learned that lesson (again).
Have you ever asked a client (possibly your boss) how fast some feature of the software you're building needs to be? The answer is "as fast as possible". That used to frustrate me because it seemed evasive but now I realize that it's actually not a bad answer. The problem is the question which is focused solely on the software itself.