If you can get an old pc and set it up as a smoothwall. Some routers will die when you try to share files / play games at the same time :S Also get multiple switches if your doing it with more than 4 people i use at least 2 for my 10 person lans. Also plot out what games your going to play.
Whenever I have lans we tend to get bored around 5:00 because we played all of our games and we just got bored. So get a bunch of games to play.
Also if your gonna play games through steam connect the LAN to the net for a bit until everyone has logged on to steam since its a pain in the ass to get everyone synced at lans :S
Also plot out how much space you have. If its in a house make sure you have enough space and that its not going to annoy sleeping parents. Make sure to take inventory on power strips, network cables, energy drinks, and Networking hardware. And another thing: BRING A LOT OF LONG NETWORK CABLES!!!! Also plot out where power cables will be coming from and where to place the switches / dhcp server.
Well theres my advice. I have hosted around 10 lans and I just had one the other night. Good luck to ya.
<--The easiest way to set up your own router / dhcp server.