In Game, All The Time
Many weekend long games might talk about the idea of being "in game the whole time". Shadow Accord may do it differently than some. When we say "You're in character the whole weekend", we mean that you're really, *really* in character. You're dressed in your garb, you're doing what your character would do, you think what your character would think, when you are alone or with one friend you know out of game...you're still role playing.
Some come from the tabletop gaming background or from other LARPs who more closely mimic the tabletop gaming genre. In those games, the basic idea is that you are there as a unit of people who have ST-like things happen to them. The players are there to interact with Storyteller's story, and then secondly with each other. This encourages a system where the players will roleplay with one another between ST-driven scenes but the point of the game is those scenes that are delivered to the players.
SA (and it's predecessor, MT) don't work that way. The point of the game is the player characters. The STs are there to provide atmosphere. They make a rational game occur around the players. They make sure that the rest of the non-player world does all the things they need to do (exist, react, etc). The rest of the time, it's up to the players to create the game they want to play in.
You'll hear the phrase "When you're bored, your character is bored. When you're hungry or cold or tired, your character is hungry or cold or tired". Because you are always in character, your mood and sensory experiences are the same that your character has. Since the STs aren't there to run the game for you, it's up to you to find something to do when bored/cold/hungry. It's your responsibility to feed yourself, get a cloak or find some entertainment. All of these things can be done in character.
Lots of folk hear about how we're in game all the time, because really we repeat it often, but even the ones who hear it over and over again don't always get it right away. That's ok. None of us really got it at first. The key is being willing to be flexible, to learn and experience. What would your Gangrel do when he's bored? Would he stir up trouble? Find a snack? Take a nap? Spy on the Werewolves? How about your Black Fury? Would she practice fighting? Cook a meal for her pack? Go find a weak male and pick on him? Might your Chanteur compose a song or go looking for inspiration? Perhaps your commoner would go get another lock for her door.
Every time you step out of your character, you pull yourself out of the game. Sometimes people need to decompress from a tense situation or just need some breathing room and there are OOG spaces around for those times. But every time someone cracks an OOG joke or someone starts talking about their World of Warcraft character with a friend because they think they're alone, they've lost some of the game.
Those two things are even worse because they affect someone else. Even when you think you might be alone, you never know when someone might be around.
Spend the entire game in character, in thought as well as deed. It's not easy, in fact it can be really, really hard. But it's also amazing and it's the thing this LARP provides that very, very few other games can... full immersion.