Beginning
The first thing you need to do is to have a beginning, middle and end and maybe a Coda right at the end. The beginning needs a description of the main character, surroundings and about the characters. The main character does not have to be in the first chapter or paragraph; they can be brought in halfway. A good way to introduce a character in an action sci-fi movie may be an eye-scan which says their name at the end.
Middle
The middle needs complications, series of events and maybe the description of the surroundings and the main villain(s). Action movies often have car chases or shoot-offs so killing of a couple of semi-main characters is an option here, as then you can describe how a character feels and how (s)he releases his or her feelings.
End
The end is the hardest part. It needs a dramatic ending with lots of suspense and action. The main character can die in this part or can solve all complication and defeat the enemy and have sad little “happily ever after”.
Coda
With this part it most likely be set in the future, so if your main character dies it could be the funeral or if your main character falls in love it could be a wedding just let your imagination run wild.
