If you are an independent filmmaker you probably see yourself primarily as a creative person. The major skills you focus on developing are around screenwriting and directing and you aren’t probably very interested in developing business and marketing skills.
Orson Wells once famously said many years ago that filmmaking is 2% about making a movie and 98% about hustling. That is probably even more true today.
Before you start filming you need to secure financing, contract with actors and crew, get location and equipment, and a lot more details that all involve business and marketing hustle.
After your film is finished you have a big job ahead with running a promotional campaign which may include getting into festivals, a website, PR efforts, etc.
It is very important that you not overlook the amount of effort and hustle required to survive as an independent filmmaker. The glamorous parts of filmmaking are a very, very small part of the whole picture.