How do the pros make that totally new synth or crazy sound effect?
First, start off by learning a technique and understanding how it works. Then, take the time to get comfortable with it and be able to apply it regularly. Once you have a decent grasp on the concept, it is time to bend those rules. Go against the grain and try something different.
Many established producers already apply this technique regularly. They set trends and norms by thinking outside the box. Instead of doing what everyone else is doing, they add their own unique twist to it.
By learning the core fundamentals of a standard practice, you are not flying blindly into the unknown. You start to envision what may happen when you do something that is against the rules. This is not the same as random experimentation, which can be very rewarding too. Instead, this is careful application of theories that you develop with experience.
So load up your favorite plugin or effect processor and try something new, get creative and find your sound.