Any creative endeavor, be it in the arts or even business, is all about passion. If you are passionate about your topic, be it a documentary or a narrative film (short or feature length) the rest is simple. Just keep in mind that simple is not the same as easy; if something is easy we don't place any value upon it.
When it comes to filmmaking it is all about preproduction. On the artistic side it is producing a script that will capture the audience, the cast and crew. On the technical side it is all about mapping out the budget, the scheduling, the visual & audio gear and a thousand other details. As artists we must be well-versed both creatively and technically. The more technique and experience you have the more creative you can be within your budgetary constraints.
As the director you are a benevolent dictator. Your word is law, but an open-mindedness to the technical and creative contributions of your cast and crew is essential. You can't know it all and you can't do it all, not matter how talented you are.
So pick your passion, plan carefully and surround yourself with like-minded people.