I've got one of my own, but first...
Don't bury the lead, do not give options if there are none and do not spend too much time describing the furniture if the furniture is not important but the painting over the fireplace is.
This. You can get yourself lost so easily by describing the wrong thing in too much detail, or the right thing in not enough. I consider myself a very experienced DM, and this is probably the mistake I make the most. When you (me!) get wrapped up too much in your own (my own!) beautiful, stylish prose, the players will seize on the thing you weren't expecting every time.
When the PCs zig instead of zag, and I've got nothing in the tank, I throw it back on them.
This. Player input can elevate a session, and buy you time to think. In a recent session, PCs were hired to steal a thing back from the guy who stole it. They decided to investigate the thief to find out
why he stole it. "Who are you approaching to find your answers? What do you hope the answers will tell you?" I got then to tell me where they were going and what their hope was, then built it into the scenario.
TAKE NOTES! I cannot stress this enough! TAKE. NOTES. Several times I've had to just admit, "I no longer remember what happened. We'll figure it out."
This. I know I said 'this' before, but... really. This. Make notes of your ideas, player ideas, your actions, their actions. You can draw on those later, but even if you don't, you won't be surprised when it comes up. The players will always remember that one thing you let yourself forget.
Don't get wound up overthinking this stuff.
This. Go with your gut. Don't be afraid to take a minute, but don't make it ten minutes while they always wait.
Depending on the group dynamic, don't be afraid to remind players if they aren't taking something into account. But just once.
"Are you Sure?" - Use this sparingly. But when something is
really out there, and you haven't a clue, scratch your head and go "Are you
sure you want to do that?" Give them a chance to reconsider. Again... sparingly. If you do it all the time it can lose power, or begin to seem a little railroady.
Okay, this is the one that is hardest for me. All caps for emphasis....
RELAX.
It's a game. Enjoy it. That doesn't mean we don't take it seriously, or that we don't try our best. But this hobby of ours is a game, and YOU are also a player. Let them make their mistakes, don't be afraid to make yours.
Of all this, I think my favorite thing to do is get the players to tell me what to do.
Redhammer's Advice above is great, and some of my best sessions have come when I had the players guide a session like this.