What it all comes down is knowledge and experience. Knowledge and experience come from practicing your craft on a regular basis.
Whether it's sports, or the arts, or business, or the sciences, no one starts at the top. But, for some reason there are many, especially in the entertainment arts, who think that they can skip the interim steps. If someone handed you a guitar you would not immediately start playing like Jimi Hendrix. You need to learn to play chords and lines, you need to learn to tune and maintain your guitar.
Hey! I learned six chords and three lines! I'm ready to record an album and do an arena tour!
Not very realistic, is it? Even Hendrix spent many hours practicing and playing many, many crappy gigs. Yet some writers think that their first script is a summer blockbuster or an Oscar winner or both.
Do some shorts. Work on the projects of others. Build your base of knowledge and experience, start building your network.
I have a couple of ideas on how film works with the little experience I have in a media firm where I work full-time.
I would wager that you really have little idea of how making a film works. As Thomas Edison is quoted to have said, "Success is 10% inspiration and 90% perspiration." Even in my craft of audio post I spend a great deal of time organizing before recording or editing one sound. On a feature, depending upon the genre, I may take one or two weeks doing nothing but prep work. I need to coordinate with the director and/or the producer on scheduling and budget. I have to create cue sheets for DX (Dialog), Foley and Sound Effects. I have to co-ordinate with the composer. I may have to schedule ADR sessions. I may have to rent gear and into the field to capture the raw material for sound effects.
Then I can start working the audio, which is what I really want to do.
Every other film craft requires just as much, if not more, prep before getting to the fun stuff - like actually shooting. But shooting your film will not be fun if you don't do a thorough, extremely detailed preproduction. And don't forget about having to do all of this within the constrictions of your budget.
As
Sweetie mentioned, there are many people more than willing to take advantage of your inexperience. Only by expanding your knowledge and experience base will you learn to avoid these types of people.
I did lots of shorts for free when I started out in audio post. I made lots of mistakes - fortunately I could correct them before they left my studio - but learned from each one of them. By the time I started charging for my efforts I had worked most of the kinks out of my process, increased my efficiency, and my studio had become an instrument I could play instinctually.
Get out there and work on other projects. Learn, learn, learn. Network, network, network. And don't be upset if you never make your own film, as you may find that one of the other film crafts is much more to your liking and more in line with your strengths. I was never a song-writer, but I could arrange & produce other writers songs, and get musicians to give great performances. So I may not have written it, but it was a better presentation because of my efforts. In audio post I have not saved a project, but have given a little more focus and clarity. Once a short project was completely re-edited because of my suggestions. (If you want to know what I did, I used DX from an extended scene that had been shortened [protagonist talking with his psychiatrist] as a sort of voice-over to connect other scenes as the overall flow of the project felt a bit disjointed to me. They re-edited to take advantage of the idea; the therapy session became the reason for the flashbacks.) The feature I worked on a few years later for the same director/producer team took much more advantage of sound-for-picture, and I was even sent a script and consulted a number of times during preproduction. The result was really fun to work on.
Well, the lock-down has got me rambling again, so I'll stop here.
Peace, and good luck!