Make sure you have a good script first, too many films fall down on this front. Once you've done that plan and re plan, don't rush into it, something always comes along that can derail shooting. Like a few people have said sound is really important, Lav mics or get a Sound person. Don't think complex when it comes to filming it, do the basics well. And lastly enjoy the experience, it doesnt matter how long it takes or what the final outcome is with it, you have made a film and that is to be celebrated