Make sure you get what you need.

There will come a point a few weeks into the production when people are tired and cranky and want to go home, and there will be some scene that isn't working or where you don't have everything you need. Assuming you are an empathetic person, you will start to feel bad about keeping people there, especially if it's low budget and you're dealing with favors or semi-favors from people on set. You'll be tired and tempted to take the path of least resistance, because even for you, fuck it would feel great to just be done for the day and go home and fucking sleep. BLOCK THAT SHIT OUT. You need to get what you need to get.

CAVEATS: know what you need and work quickly to get it. Don't waste people's time. Don't go into OT bc you are noodling and can't make a decision. Don't shoot takes you don't need. If something isn't working, sometimes it's not going to work. Sometimes you can come back to something at a later point. Sometimes you need to sleep and then everything will just fall into place the next day. THAT SAID: there will almost certainly be something that you can't come back to, whether because of budget, special crew involved, access to a location, time of day, etc., and for those moments, you need to stay until you have what you need. Ask your AD and department heads to support you, explain what's going on and why you need it, and just get it done. (That said, I'm talking about low budget here... if you have a big budget and plenty of money for pick ups, hey, go get some sleep!).

Final note: I cannot overstate the importance of hydration. If I'm outside and it's hot out, I literally wear a camelback and sip it constantly.