OK- Here's just a personal opinion.
I think the first step is motivation. WHY are you going to do this?
It is a journey that may be filled with stress, financial obligation, self doubt, time commitment, possible disappointment, frustration, hard work and study. It will likely also be a trip with experiences of elation, self satisfaction, personal growth, new curiosity, ego boost, fresh lifetime friendships, professional expansion and excitement.
There's no single reason why someone would be willing to go through this possibly hellish journey, but the combination of reasons must be personally compelling. I think you should be at a point in your life where something inside you just compels you to take up this challenge.
It could simply be ego. "I know I can achieve this standard"
It could be a need for self-testing. "I think I might know enough to pass"
It could be a need for community. "I think I belong with these people"
It could be curiosity. "I wonder what it would feel like to have top accreditation?"
It may be professional. "If I'm going to ____ , I need this accreditation"
It may be a need to give back. "AIFD is the world's top floral education source"
It may be the challenge. "I think I can, I think I can, I think I can"
There are SO many more reasons than I can list, and likely your inspiration will be a combination. A wrong motivation would be just thinking it will get you more business success. (It probably will, but that's not a good reason in this case IMHO.)
Strive to make it the first time, but expect that it may take several expensive and exasperating attempts before you pass. You'll learn through failure how to overcome the obstacles that defeated you. Each of these lessons will serve you in your career, such as learning to perform under pressure. Such as being able to self analyze your own design and improve your proficiency. Can you take detailed instruction and return back expected results?
Whatever the reasons for starting this journey, they should come from a burning place inside you. Anyone who makes a casual commitment is probably wasting their time.
What do you get in return? You join a special group of like-minded professionals who are interested in continued learning and improvement of their art and their craft. You get regular access to tips and techniques developed by those who are influencing the direction of international floral design. You will bond with others who strive to achieve their personal best and who feel a need to help educate others in the industry to reach for a higher standard.
Do you have that personal internal desire?
Why are YOU doing this?