You can list your domains on one of the many auction sites (Sedo, TDNAM (charges an annual fee), and many independents. Another hot tip would be to list the domains you'd like to sell right here on NP in the Domains for sale section: Just click on "Marketplace" and choose the appropriate thread for your sales.
However, while you're waiting for an offer to come in, which may happen immediately or never, or anytime in between, i heavily encourage to at least park your domains to retain the option to make at least a few cents here and there in the meantime.
If you need any parking help, shoot me a PM.
IB