The first step in the contribution process is to open a ticket. Please do so through JIRA and not through GitHub. Tickets can be created by anyone, whether or not they have signed a Clojure contributor agreement. It is OK to create a ticket and submit a patch at the same time, but please be aware, if the ticket is later rejected, the time spent developing the patch will be lost. Therefore it is recommended that coding on non-trivial patches should be postponed until after the vetting process. One possible advantage to submitting a patch before the ticket is vetted, is that it might be vetted and screened all at once by the screener, if they choose to do that, saving some time.
If you have questions about whether some behavior of Clojure is a bug, or submitting bug reports or enhancement requests, please ask on the clojure Google group.
You need a Clojure JIRA account to create a ticket. Go to the Clojure JIRA page and click the "Log In" link near the top right of the page, then on the next page click the "sign up" link. If you see your name instead of a "Log in" link, you already have an account and are signed in.