Step 1: Create a utility library.
Step 2: Require it in your app.
Nothing sets a utility library apart from any other type of library. They’re all libraries.
Here is a list of utility libraries authored by experienced Clojurians:
Personally, I tend to separate them according to their dependencies. For example, utility functions that don’t require any dependency, that are pure Clojure, go into a general-purpose utility library with no dependencies. Functions that are more specific to a line of applications go into a separate library. For example, I have a small utility library devoted to ring applications, with a dependency on ring.
Here is a quick overview of how I organize things, but remember that there is a lot of leeway and utlimately it’s up to you.