A fairly beefy external power supply is a handy thing to have. I use a 12 VDC jumpstart battery with my little ETX-60 through a 12VDC - 9VDC converter I picked up at Radio Shack.

A 2x Barlow might come in handy. The built-in Barlow is okay, but it requires a lot of turns of the focus knob to refocus when you switch it in or out, an external Barlow doesn't seem to shift the focus as much.

Other than that the usual suggestions; read the manual, visit Mike Weasner's Mighty ETX Site, calibrate the motors, and train the drives.

I know I voted for the ETX-90, but the ETX-80 is a fine little scope and the -80 and -90 are different enough they compliment each other nicely rather than compete against each other. I'm sure you'll have a lot of fun with your new scope.