1) NEVER use real names. If the FCC can't get a real legal name to attach an action (fine) to, they don't have any leverage to stop you. In your group, always use alias's, even day to day. This is your best protection against getting shut down long term. You may get shut down short term, but if they don't have a name, you can come back over and over again.
2) If you're running hot (i.e. a transmitter IN the studio you're broadcasting from), eventually, you WILL get a visit from the FCC. DO NOT let them in without a warrant. Regardless of what they say, they CAN NOT come in without that warrant.
3) DO NOT talk with them. Say "I have nothing to say to you, you're on private property, please leave". Even if they have a local cop with them (which is likely) you don't have to let them in and you don't have to talk with them. They are generally very good at drawing you out and getting you to say things you'll regret later. Don't give them the chance. Don't talk. Period.
4) If they do have a warrant (which is highly unlikely if it's your first visit), let them in. The first visit is a 'search and warn' mission. They want compliance (i.e. shutting off the transmitter) more than anything else. They'd like to get their hands on the transmitter but can't without a warrant (again, something they are very unlikly to have on the first visit). Let them go where they want, but take pictures and record (with a tape or video camera) everything they do. This is useful for talking to the media later and ensuring they don't do anything particularly rude or illegal (which they are capable of.. they are excellent 'social engineers'... getting things through hook and crook they can't get legally).
In general, the FCC agent's are good guys in a bad situation. Most of them are no happier to be there than you are. To them you're a very small problem taking up valuable time. There are only about 400 (I've heard as little as 200) field agents that can do this kind of work and they've got alot of other things to worry about (telephone companies, cable companies, cellular phone companies, that remote control for your garage door opener.. anything that lives in the electromagnetic spectrum that they regulate). They are most likely there because someone (usually a local radio station, usually a clear channel station- they are the most aggressive) complained. Be polite, don't talk to them, turn off the transmitter after you ask them to leave and shut the door and wait a day before going back on air.
Next, if you choose to continue broadcasting from that same location... you're now at risk of a raid (with a warrant). They know where you are, and they can go to a judge and get that warrant (usually to take all your equipment.. and I mean ALL of it. If it has anything to do with sound,they'll take it. Your stereo, your tv, anything they can... although all they really want is the transmitter.. they'll take it all because it makes it harder for you to come back on air).
Your best bet after the first visit it to MOVE locations. That resets the process. They're back into 'warning only' mode.. and the chances of getting a warrant, if you're in a different location (raising the potential that you're a different set of pirates...) resets the legal process, for them, to zero.
So if you move EVERY TIME after a visit, chances are, you'll never get shut down. Just harrassed. So plan for it. Have a new location planned and ready to take you when you get a visit. Move your station overnight and come back up the next day. They'll be back, but it's likely to be 3-6 or even 12 months later.