The easiest way to contribute is to donate. The costs of running the site are covered by the Common Lisp Foundation.
Thank you for your support!
If you would like to contribute by donating your time, please let us know (through a mail to this mailinglist, for example). There are currently a few projects that need attention, and we almost always can use a helping hand.
Two projects waiting for volunteers are
Also, if you have a cool idea for the site, feel free to let us know.