I flaked on a photo shoot but I am not a flake.
I don't care who you are or what you are, a model or a photographer. Sooner or later something will happen to cause you to not show up to a shoot or cancel at the last moment. This is commonly called flaking on a shoot. But you are not a flake, how do you respond.
The first thing that you should do is apologize honestly and sincerely. Not everyone will accept your apology although most will. Try to reschedule immediately, do not let it go by unless you meant to not show or cancel due to some other reason that is more to do with not wanting to work with that particular creative.
It does happen that even after days or even months of planning you come to the realization that the person you agreed to work with is not for you. Cancel early, and if you have to cancel for another reason, do so early. Giving the other person or group of people enough notice is just polite, regardless of your reason.
Now, if this is a paid gig, canceling and especially last minute cancellations will hurt you where it hurts the most, in the bank account. If you are hired for a job and decide to quit before your first day or for freelancers the day before the gig typically you will not be offered another opportunity with the employer.
What I have heard told to me for excuses runs the gamut from oversleeping to death in the family. Some very valid and then some pretty lame. I have had years of real work experience and time in management and typically I know when it is a lie. So will you, but as my wife reminds me when it happens to me, let it go unless you are paying them.
Avoid saying things like, I was so excited to work with you. If you were that excited you would not have overslept or planned better so you would arrive on time. The most precious thing to a person is time, there is only so much of it. Don't treat it like you were not in the wrong, just accept it and try to make amends. It is your reputation, and a bad one does spreads like a cancer with modern social media.