If you have excess fat and could afford to lose some weight, then just do it, there’s absolutely no need tor any preparation, just start. You can try eleven days, but even if you manage just seven days that would be enough time for your body to heal.
It’s usually just practice. Keep going for longer each time. I started with 1, went to 3, went to 5 and then 7 is my record. But some people just cold turkey and go for it (so long as you have the body fat ofc).