As others have said, re-capping the components, removing and replacing the battery, and looking at other moving parts such as the floppy gear are all excellent steps to take. (The only exception is if someone already re-capped those boards, re-furbished the floppy drive, or the battery was already pulled).
All of the above safety advice is great as well. I've usually let my pre-SE boards sit for a week, which has always discharged everything, but the proper discharge procedure is still highly recommended. (Keep in mind my experience falls under the law of small sample sizes; even though I've worked on about a dozen pre-SE computers, that's still 12 out of thousands).
Be sure to wash the boards before re-capping. I also advise removing any dust from the case, fan, etc. You can also give the case a bath in Endust for Electronics.
There is one other thing to prepare for: the fun you'll have with this machine. The SE/30 is a blast--it's got a ton of power in a tiny package. Go ahead and test its limits--I once got an SE/30 to play an MP3 file on its internal speaker, which was a lot of fun just to do as proof of concept!