look after your people
arrive together, check in through the night, leave together. decide it before you go out.
Agree three things before anyone leaves the house.
Who is counting heads. Not a vague sense that everyone is fine. One person who actually knows where everyone is, and swap that job through the night so nobody carries it alone.
Where you meet if phones die. Pick a physical spot inside the venue. A pillar, the left side of the bar, the smoking area gate. Phones die, networks drop inside basements, and "I will just text them" fails exactly when it matters.
What time you are leaving, roughly. Not to hold anyone to it, but so nobody is left guessing at 4am.
Through the night, actually look at your friends. Someone who has gone quiet, stopped dancing, gone very still or is sitting down alone is telling you something. Ask them directly. "Are you okay" gets a reflexive yes. "What do you need right now" gets an answer.
If someone is unwell, get them somewhere cooler and quieter and stay with them. Tell the venue staff. Security and bar staff have seen this before and would far rather help early than deal with it late. You will not get anyone in trouble by asking for help, and waiting because you are worried about that is how a manageable situation stops being manageable.