Almost always use your interest check post for your OOC. It saves you the trouble of having to make a OOC (unless there is a lot more to add).

Most people in an interest check are likely to flake on you. You may have ten people interested but maybe 5 or so will still be around for the RP, and even less are likely to stick around for the long haul.

Don't be too strict or too lax. You don't want a RP to go fully off the rails, but you also want to keep your players from rioting because you're forcefully railroading them through the plot. Players are distracted by someone? Tie them into the plot somehow--perhaps they've been sent to assassinate the players or something like that.

Make sure to read sheets so your players can't try to pass something vague as part of their sheet. I'm normally not picky on this, but if people say they're strong, it's still hard to imagine them lifting a bus without superpowers. None of that "but the sheet says they're strong!"

Also, practice makes perfect. Being a GM sounds daunting at first, but you honestly won't get comfortable GMing if you put it off because you're afraid of actually GMing. It's like facing your fears, essentially.