Add the following to ~/.ctags (thanks, xzj / clojure.ctags):
--langdef=Clojure
--langmap=Clojure:.clj
--regex-clojure=/\([ \t]*create-ns[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/n,namespace/
--regex-clojure=/\([ \t]*def[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/d,definition/
--regex-clojure=/\([ \t]*defn[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/f,function/
--regex-clojure=/\([ \t]*defn-[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/p,private function/