This is probably the most stressful part for me. Here are some tips that you can use so that you aren't freaking out all the way until shooting day!
Talk to everyone. Constantly. Be in touch and have your phone on you at all times. You might think you are being annoying by constantly texting people if they know the location, if they are bringing the props you asked them to supply, or what they should wear and how they should look for the shoot. I know for a fact that my friends have thought I've gone overboard asking and reasking... I just want to be absolutely sure that everything will go smoothly. When you feel like you could just sit down and cry, take a minute and write everything down. This is so that you can feel reassured, and I know that its helped me. The night before the shoot you should have your camera battery charging, as well as your phone, everything should be neatly organized so that in the morning you can pack it all in the car and get moving (or put it in the car the night before to get extra points!). If you do decide to shoot in a place that you haven't scouted, just be mindful that you may not get the exact images that you made up in your head. I went out to an area of Venice that I'd never been and we got great shots but it wasn't at all what I had planned on doing! If you have scouted and you know precisely what you want to get, make a shot list. The day of the shoot it is so so easy to forget the weirdest things. I have gone to shoots and the one thing I wanted to get a picture of never ends up getting photographed! A good trick that I use is when I get in bed I will close my eyes and make an imaginary list of things in my head of what I need to do the next day, that way the moment you wake up you've got the motive to get some great shots! One tip that I recommend to stay calm on set is, take your time. I can't stress this enough. It will feel like the clock is breathing down your neck but it will be so much more rewarding if you really take it nice and easy, getting every shot to perfection! This should help all you over thinkers like me! Most importantly have a great time!