Have you ever been to a low level meet before?
Gymnasts aren't allowed on the floor before general stretch. When general stretch starts, all the kids usually take a few laps running, arm swings, etc. Then, they find a spot on the floor to stretch. If there is no room on the floor, go to the vault runway or bar mat.
We do a kind of shorter stretch at meets. Not too short, but shorter than usual. You'll be called away for a coaches' meeting. If you're by yourself, appoint an older kid to lead while you are gone. Explain the importance of behavior at meets and how judges start forming their opinions during stretching so stretch your very best to impress them.
Disclaimer: I do not believe this to be true. However, I've told it to every group I've ever had.
While you're at the coaches meeting, ASK QUESTIONS IF YOU DON'T UNDERSTAND.
I would probably call the meet director ahead of time, explain that this is your first meet, and ask for the format of the meet if not indicated. Also ask if there will be a march in, or if the kids will just be announced at their starting event and wave in introduction.
Beam is the only thing that can really be tricky, if they do the warmup, compete, warmup, compete, etc. Basically, two kids warm up, then the first kid competes, then the third kid warms up, then the second kid competes, then the fourth kid warms up, then the third kid competes, etc. It can be confusing, but it's really not, if that makes sense.