Sometimes letting go and being in the moment is the only thing that can prevent greatness.
How To Prepare
Everyone is different. What it means to prepare for one person may not be the same for the next. However, one of the most valuable things that anyone can do before a session is to get plenty of rest. Lack of rest can throw off the balance of not only yourself but also the shot. Unless you want to inform your audience that you are a part of the "team no-sleep" crew, you might want to plan ahead for plenty of rest... and hydration.
Make sure you have everything you need before coming to the designated area. Some things are not important as others and it's not uncommon to have to go back and forth for certain reasons during your session (phone call, potty break, collective stroll, ect.). However, you don't want to reschedule your session at the last minute because you forgot something or someone.
At The Shoot
Starting right on time is a realistic expectation (sometimes life does happen but please be proactive in communicating any difficulties that may arise).
During the session, be prepared to let go of anything that is holding you back from capturing the shot you desire. At times, those hidden emotions can be caught on camera. Eliminating those distractions can increase the output of quality photos.
Some things go without saying. However, professionalism is of great importance along with fun. A healthy balance will always produce the best results.
"Treat a man as he is and he will remain as he is. Treat a man as he can and should be and he will become as he can and should be." ~ Johann Wolfgang von Goethe
Be ready to follow. Photography is more than just give and take (you giving orders and me taking photos). There are things that I may see that you may not. Ultimately, it will be you that decides what photos work best for you.
Therefore, enjoy the moment and let's capture greatness.