Some people tend to starve themselves at LAN. Make sure to eat decent food at least once per day. An easy way to make sure is to eat breakfast somewhere in the morning before going to venue. The NEC has some places inside the building where you can buy non-junk food, but for any LAN it always helps googling nearby shops and restaurants to your hotel.
Also drink water!!!
Try talking to people. Asking their aliases is a good opener if you don't know where to start. If they're from the BYOC area, ask them how their games have been going. It's relatively easy to find people you've interacted with online before. Especially if you spend a lot of time on tftv/twitch
Insomnia splits the viewing area from the BYOC. You can have someone from the BYOC give you a guest pass, but there's not a whole lot to do there usually. BYOC people stay in the area throughout most of the day until the later evening when they go to the viewing area to watch upper/lower bracket finals and drink.
In general there's not much to do in the BYOC if you don't have a PC of your own. Plenty of people to interact with in the viewing area, even when the BYOC people aren't there.
(In this regard Copenhagen Games is an upgrade. BYOC isn't closed off from viewers so it feels more like 1 big community sitting in a single area)
If you know some people on your friends list are going, definitely send them a PM beforehand so you can attempt to find them at the venue (setting a meeting place/hour beforehand rarely works out at LAN, but at least you'll know to look out for eachother)
You'll be watching a lot less TF2 at LAN than you would've at home
edit: thread died but might as well add something in case people are looking for info
Insomnia
*In the BYOC it's a free-for-all of all games. Some TF2 circlejerks will attempt to sit close to eachother, but you'll have to ask around to find many teams and individual player spots. It's a big area with hundreds of people, most of them non-TF2 players
*Main reason to visit the BYOC as spectator is to watch player POVs
*Just ask around if you want a BYOC guest pass. Any BYOC person can give out 1 guest pass to 1 spectator (or was it 2? don't remember). They're partially responsible for the shit you do so don't be an ass
*The production/viewing area is at the edge of the BYOC. Sort of integrated in the BYOC area. The viewrs sit outside the BYOC fences with screens set up next to the production for watching the casts. We usually are next to one of the stages (local LoL and cs:go mostly, not the mainstage) which will look very empty yet have many more chairs than our ghetto "stage". We usually steal chairs from there.
Copenhagen Games
*Here the BYOC for TF2 is all condensed into 1 area. Still need to ask around a bit to find people unless you'd recognize them by looks, but way easier than insomnia
*Viewing area in 2018 was fine, in 2019 there were issues with fire safety (viewing area'd block 1 fire exit and a big entrance for firetrucks) so we didn't have a viewing area for the first day after we pestered the Copenhagen Games staff for a full day. Should hopefully be better coordinated in 2020 (this isn't really advice in any way. But might as well throw the info out there)
*NO CASH AT THE EVENT. bring a card. 2 out of the 3 food trucks outside the event accepted cash. burger food truck and all the bars/food inside was card only