I won't tell you strictly how to write, because it would be like putting creativity into some kind of a frame.
Watch films, read books, comics as many as you can. By doing this, you will learn what is already used for a million times. Don't reinvent a bicycle unless it's completely different from the original idea. Be original.
Learn from mistakes of other people. For Example: one act can't last for an hour. Put some cool sequence better, like imagine that in Rocky, training goes for 40 minutes, eventually it would get boring. I seen a movie(two hours long), there the character is building a house for an hour and then goes to the party...
Write interesting characters, whom is easy to believe. Give him a personality, and all of Personalities acts different in different situations for a different motives. Like in "twilight"(in the movie, I didn't read this series), Bella has no personality. She just can't say anything to Edward except "I love you", and the only thing she does goes about Edward. It seems like an empty slot who loves Edward. Edward also has the same problem, his only personal qualities: is a vampire and loves Bella.
Plot should be bonded very well, most of the time one scene should give a birth to another. It can't have a gap, unless you want one. Like in "From Dusk till Dawn", the absurd of the movie crack me up, every time.
Also try to avoid logical mistakes. Example... "Green Lantern: first flight", Guardians argued for 4 or 5 minutes about Hal Jordan evil or not. Then they remembered that they have telepathic powers so they can find out. It's like forgetting our ability to walk.
