If you are just starting to become interested in making movies, you have to learn them. Practice with a camera, or without a camera. Your first movie might be a little rusty, but that's okay. Making decent movies takes time. It took me a few years to make a movie I was quite satisfied with.
Ah, the cast. Probably one of the hardest tasks in making a movie. You know why? The cast is a whole different part to the movie. If you were to make a movie by yourself, it would be quite easy. You could film whenever you wanted to, and how you want to. Now, with a cast, a problem erupts. You have a cast with of two, that's quite easy. You can have an easy filming schedule, and you only have two actors to worry about. Now, if the cast gets bigger, you're going to run into frustration. At first the cast will probably go with whatever you say about the movie. But then, they come up with their own ideas, some you might love, some you might want to throw in the trash. And if you disagree with a cast member, they will tend to get mad, and that makes the movie quite a bit more difficult. And plus, when you have more cast members, it will take longer to have a filming date. If you want to film one day, another person can't. If you can't film another day, someone can. It goes on, and eventually the movie is forgotten after a few weeks. But a cast can be good, because you can have a variety in the movie. What I don't like about the cast also is sometimes they can be too demanding. They want the lead part, they want more to do with the movie. That causes another bump in the road.
Probably one of the most dissapointing parts in making a movie is when the cast loses enthusiasm. You have this big idea planned for the movie, and everybody in the movie likes it. You have everything planned, and after about a week of not filming, the cast sometimes quits on you.
One big mistake that many acors make is they put to much pressure on themselves. You don't have to have every one of your lines memorized, just learrn 'em as you go along. Acting stinks when the actor is under pressure so just chill.
Another big mistake actors make is getting into fights with directors. This is just about the worst thing you can do. It slows the move down, it makes you mad, it makes the director mad, and it pisses of the rest of the cast. Don't think that you have power over the director just because you are good at the part. He can find somebody else if the movie seems to be good enough.
Just because you respect the director doesn't mean you have to be a total pushover, It's okay to suggest stuff to your director, he might like your ideas. Take this website for example. El Zacho went up to Bryan and said: hey, I hear geocities lets you put movies on your site. Then the whole idea spun around for a little while and ended up as this site. Pretty cool, huh? But you can also make the director think that you are trying to take control and that might make him mad.