1.  People have actors in movies that don't have goals, if you don't have a character who knows what they are doing and a clear goal of what they are doing, then it won't be a good film.  You can fix this problem by making sure your actors know what they are doing, make sure they have set CLEAR goals for themselves, and make sure they aren't confused with what they are doing.

2.  Under cooked Scripts is also a very common mistake, people just want to rush into the movie without making a good script for their film.  By doing this, they are unprepared for making the film and they won't know what they are doing because they don't have a clear idea of what the movie is about.  You can fix this by, before going out and shooting, make sure you have a good script, making sure your actors now the script, and overall being more prepared.

3.  Bad Sound is also a horrible mistake, it doesn't matter if you have an amazing film with great lighting, good shits, and great actors, if you have bad sound, the audience will not tolerate it.  You can prevent this by making sure you check your mics once or twice and also by keeping your mics as close to the actors AS POSSIBLE.

4.  Poor casting choices is also a very bad mistake, in many cases, you will see a 16 year old trying to play some drug lord or their friend trying to play your mother.  You can only do so much, stretch it out, until your audience sees through it and doesn't believe it.  In fact, 90% of directing is casting, so you NEED to make sure you have PERFECT casting choices to have a good film.  You need to make sure you CAST WITH CARE because when you have good casting you will have a much better film overall.

5.  Poor Shot Composition is also a very common mistake, in many films they are cases where there is just a lot of empty space taking up room.  It just gets boring because there is a lot of empty space and your audience will daze over and stare at it instead of looking at the action.  To prevent this, you can use the rule of thirds, by splitting your shot into three different areas and have your action in the middle of the three, it will make your audience the most intrigued.  It might not seem important, but it is, to have a good film, you need to make sure you include the rule of thirds into every take.

6.  White walls are very common in many shity films, having a white wall behind your actors and the action is SO BORING, it makes your audience bored too.  Not having some color or something in the background will make your audience very uninterested.  To prevent this, add some color, go out and buy some materials to make the white walls much more INTERESTING.  The more interesting the background, the more engaged your audience will be and the better your film will be.

7.  Bad lighting is also a very bad mistake and it is one of the most important mistakes you NEED to correct.  If a film is dark with no lighting, first of all, you can't see anything and second your audience will get so bored so fast.  Lighting is not an option, it is a requirement to have a good film.  To prevent this, make sure you bring your lights, have batteries that are charged, and make sure you add light where it is needed.  The more light the better!

8.  Another mistake is putting in unnecessary insert shots, they are when the camera goes away from the main shot and focuses on a small thing that is important.  If you put in an unnecessary insert shot, it is just unneeded and it takes up unnecessary space in your film.  Plus, you don't need a shot to describe what you are doing, to fix it,  just add it when it is really important, not when it is obvious what is happening.

9.  Lingering is another big mistake, you don't need to show the simple thing in your movie like walking through a door or walking down a long hallway doing nothing.  By doing this, it slows the pacing of your movie down and thats not what you want, you want a fast paced film that goes right to the action and isn't boring.  You want your audience to be engaged, not falling asleep in their seats.  To prevent this, you can only put in the most important shots, anything else is slowing your movie down and we just want the meat of your film, not the scraps.

10.  Having too many pregnant pauses is also a big mistake, you want your film to be fast paced and make sure you spread out your pauses, if you just have them over and over, it will make the audience very bored.  When you have a film that has a very long pause and more pauses afterward, it really slows the overall pace of your film and you don't want that.  You can fix this by spreading out your pauses and making sure they aren't all so close to each other, you want to have a few not 20.

11.  No movement is also a common mistake, when you have 2 or more actors talking to each other, you don't want them standing in the same spots talking and talking.  It just gets boring and the audience will get bored of it because there is no action within the scene.  To fix this problem, you can have your actors moving around while they talk so it is more engaging for the audience to watch.  You can see this in many Hollywood films, the actors aren't standing around, they are moving and doing stuff while they talk to each other, because that is what really happens in real life.

12.  Chit chat is also another big mistake, you will see many films that have just talking and no action, it just makes the film boring and you don't want that.  To fix this, make sure you have a lot of action in your film, the more action there is, the more the audience will be engaged with what is happening, but you need to have just enough chit chat in there as well..  

13.  Action for the sake of action is also a big mistake, if there is too much action and little dialogue, it will also be confusing for the audience to follow.  You need to make sure you have a good consistency of action and dialogue to make a good film, if you do this, you will succeed.

14.  Cliches are also an issue, too many times you see a film that starts with someone waking up out of bed and after a while of watching all these films with the same cliches, it just gets redundant and boring.  You need to make sure your film has a cliche that is original, your idea, something that has never been done before, so the audience will be engaged from the beginning of the movie until the end.  By having something that hasn't been done before, it will make your film better quality, and more engaging for the audience to watch.

15.  Weak starts are also a bad mistake, by starting with a boring beginning, the audience might not want to stick around to watch the rest of your film.  To make a good piece, you want to have a great beginning so you can grab your audience  at the beginning and they will be engaged from the first minute to the last second.  

16.  Generic music can also be bad, if you have epic battle music for someone eating cereal or fairy princess music while a fight scene is going on, it just doesn't fit and is plain awful.  You can fix this by making sure the music fits in the scene you are shooting and if you just cannot find the right type of music to use, you can always just use no music.  That is still ok, but it would be more engaging for the audience to have music that fits the scene that is being shot.