My advice, having been through film school: Do a short film first.
A short film would allow you to test the waters to see if film-making is really something you want to get into. Even a low- or zero-budget short film (and this is multiplied by whole orders of magnitude for feature-length films) takes a whole cubic shit-ton of planning and coordination with a decent-sized group of people working with you if you want it to turn out as anything other than a steaming pile of amateur s**t, because Murphy's Law and Finagle's Law apply to the film-making process in spades.
We're talking days or weeks of writing, re-writing, planning and preparation, and a group of at least five or six people, absolute minimum, for cast and crew; and that's assuming you're going to be taking on all the responsibilities of writing, directing, filming, editing and producing yourself, and not distributing them out to other people. If you're not planning on doing all of that yourself, then you're going to need even more people to help out than that.
As for what genre you should make it, rule one is: Write what you know and enjoy. After that, the least resource-intensive genres are usually drama and comedy, followed by thrillers and action. Sci-fi and fantasy are the most resource-intensive genres to pull off correctly, so try to stay away from those unless you have a means to come by the money, labor, props, costumes, and 3D/compositing software for it.
I myself am currently writing the script for an approximately half-hour long psychological/supernatural thriller about a man who wakes up from coma two years after a near-fatal accident, but instead of having no new memories from those past two years, he has memories of people he's never met, places he's never been and things he's never done in that time. Haunted by them, he sets out to find the truth and gets involved with the real-world equivalents of the people from his memories, and drawn into a series of events he doesn't fully understand.
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It takes a village to raise an idiot, but it only takes one idiot to raze a village.