From your device, if it is rooted
According to a post on xda-developers, you can enable ADB over Wi-Fi from the device with the commands:
setprop service.adb.tcp.port 5555
And you can disable it and return ADB to listening on USB with
setprop service.adb.tcp.port -1
From a computer, if you have USB access already
It is even easier to switch to using Wi-Fi, if you already have USB. From a command line on the computer that has the device connected via USB, issue the commands
adb tcpip 5555
adb connect 192.168.0.101:5555
Be sure to replace 192.168.0.101 with the IP address that is actually assigned to your device.
You can find the IP address of a tablet in two ways:
Manual IP Discovery:
Go into Android's WiFi settings, click the menu button in the action bar (the vertical ellipsis), hit Advanced and see the IP address at the bottom of the screen.
Use ADB to discover IP:
Execute the following command via adb:
adb shell ip -f inet addr show wlan0
To tell the ADB daemon return to listening over USB
Apps to automate the process
There are also several apps on Google Play that automate this process. A quick search suggests adbWireless, WiFi ADB and ADB WiFi. All of these require root access, but adbWireless requires fewer permissions.