We don't have much lemmings talking about larp, and as I am moving forward in the prep of my next game, I thought about sharing some my tips/thoughts On this thread, I will focus on the typical "2-3 day heroic fantasy larp" with 80-200 players and some faction/PvP mechanics. The larp scene is pretty huge, and not all of my points my transpose to what you play nor your local game culture. So take it as a blog post with my view on-it, which may not fit yours
Expect that the logistic team will fuck up
If the writers fuck-up, you end-up with a boring story, if the NPCs fuck-up you end-up with wrong information. But in both case you end-up drinking and eating with your friends in a costume. Not that bad. On the other hand, if the only drinkwater tap is after the orc camp, or if the cook under-estimated how hungry the player are you end-up thirsty and hungry, add the lack of sleep and the fun week-end turns into a nightmare. So please plan to have extra water/food (also a whole ham on the table is a great diplomacy tool) worst case, you end-up storing some leftover at home after the game.
Another classic one in larp with "toilets" is that the toilet end-up clogged at the end of the week-end. So plan that you may-need to manage otherwise.
Finally, even though it's not a fuck-up from the logistic, plan for any possible water and adapt your playstyle. You may have temperatures above 40 or heavy rain, and sometimes both at the same game. So have a hat in your kit, extra socks, and choose the right shoes if rain is expected.
Self care
It's a bit linked to the previous point, but as much as beer can be refreshing and spiced wine can help negotiation, it doesn't hydrate. Bring water and drink water.
Force yourself to get some sleep, Game never stops, it usually get a bit quieter between 3 and 9 but that's it. However, I would seriously advise to still try to get some sleep. It can be tempting to keep playing until the dawn, and then be dragged in the day-game. But at a point the lack of sleep will catch-up, especially when you're driving. I don't tell you to get your 8h of sleep per night, but 8h for the whole week-end isn't reasonable either.
If you're not comfortable with something, or feel that a situation is physically dangerous speak-up. Can be the battle "near the stairs" which would make sense in a real combat but is a great way to break some legs in a game, can be the torture scene which is bit too realistic. speak-up if you see something dangerous physically or emotionally, most player would try to find a reasonable way to do it.
In game
Avoid the not my problem attitude, if you catch a plot hook pull it. It may not be your character main goal, but if some "game opportunity" come to you, take-it or (especially if you play a busy character), delegate to someone from your faction.
In the same category, in case of doubt say yes, you might have missed who was the great priestess of the sun, or that you had a side quest about building an orphanage. Also, sometimes, it's obviously "a trap" but the proper attitude is so what Yes you'll end-up jailed, tortured and executed, but you'll have more fun than sitting in the tavern
On the character
Remember that combat is a very small fraction of a larp. So you don't need to play a warrior in heavy armour to have fun. There is plenty of game where I didn't pulled a sword (and sometimes didn't even carried one)
Remember that you need a character you can play for 3 days, avoid the "loner type", or the "weird accent that you cannot keep on the long term".
Try to match your character with your faction, either by asking the faction which hypes you which kind of character they need or by asking the factions who would need the kind of character you want to play.
Character do die, especially the ones with some visibility, so have a second kit ready in case off.
Gear
Thrift store are a great ressource for a beginner kit, it may not be fully period appropriate but can be a generic costume basis (linen trouser/skirt, pirate-shirt) at a cheap price (well nowadays thrift store got trendy)
Layering works damn well. get a neutral basis layer, add stuff like doublet/cape to give a style to your character, and finish with accessories. Obviously expect that anything you'll bring to a larp will be lost or damaged. Make-up and hairstyle can do a lot for a character to.
Depending on the faction/character, adding some uniformity helps a lot. 10 persons with the same green/white cape/tabard looks way more impressive than 10 persons with random costume even if each one is way better than the common costume.
Remember that you're not doing cosplay, you'll be moving with these clothe, so try to craft some robust stuff. In the same category, unless you can afford decend larp shoes and the game-site permit it, better wearing some leather hiking boots and keep your feet safe and dry than twisting your ankle in period appropriate shoes
You never have too much pouches, try to keep your "out of game" stuff in a pouch, and keep the in-game items in another.
Print some "out of game sign" so you can indicate a robber visiting your camp which crates/boxes are "out of game"
Ok time runs out, I feel like I already wrote a lot, pretty sure some of you will have stuff to add, or stuff that do not apply to their games (which is fine), so I stop the thread here