Google is pushing Android 4.2 Jelly Bean to Nexus owners via an over-the-air update, but if you are impatient, there are ways to get it sooner. The firmware for the GSM version of the Galaxy Nexus (so not Verizon's LTE-equipped version) is available for download on Google's servers. The v4.2 ROM for the Nexus 7 is also available.
For the Galaxy Nexus, you can download the "takju” ROM to get the new OS on your device. You can download that manually, which is a little harder. You can also use ClockworkMod’s ROM Manager, which is a free app download from Google Play. Either way, this will allow you to get the latest firmware on the Galaxy Nexus without waiting for the OTA update.
For the Nexus 7, the process is pretty similar. You will need to download the Jelly Bean update ZIP. You will need install it manually or use the ROM Manager app.
If that sounds like more than you are willing to deal with, then you shall have to be patient and wait for the official OTA update from Google. The wait should not be long, as we expect the rollout to happen in the next couple of day.