Plan events & scenarios, but don't plan (or even assume) outcomes. Players will surprise you when you least expect it. (For example, you can have a wolf barging into an inn, but the party could kill it, befriend it, release it into the wild, or it could even become a party member's familiar!)
Instead, determine what information players will need for the following session, and make sure they get it regardless of what path they take. (Give a lot of options!) For example, if an NPC has information that the party needs, the NPC can either tell it (if interrogated or persuaded) or may have an item on them (such as a letter) that can be found if they are killed. If the party bypasses the NPC entirely, there needs to be another opportunity for the party to get the information. (There could be another NPC, the party could discover the letter, etc.)
Communicate thoroughly with your NPCs–they are your lieutenant GMs. The more your NPCs know and can implement, the more things can happen in parallel. Also, NPCs can be running one scene while the GM (and possibly some NPCs) set up the next scene. This will make the LARP run more smoothly, be more fun for the players, and will help the GM retain their sanity!
Remember: if you plan a scenario but the players choose a different route, that needs to be OK. The scenario should be easy to adapt to the players' actions while still giving them the information they need to get to the next milestone.
The set of events should include each of the following:
Note that the order of these events will be determined by the players. If there are multiple GMs (such as with a LARP), a white board or easel with sticky notes is recommended to keep track of which of these events have happened in the session.