A good screenplay:
Beginning
introduction of characters
Conflict! What does your character need/want?
Middle (need to "up the urgency" / "burn bridges")
failure #1
increase tension
failure #2
further increase tension
failure #3
Twist (can be the most challenging part of writing)
End (emotionally satisfying / humerous)
A good screenplay:
Write what you know. Only use characters that you can get to act. Don't have students play adult roles. And don't have high school students play elementary roles. Just don't. No. NO. NOOO.
A good twist is key. If your audience anticipates the outcome, it will fall flat and disappoint.
Keep your sets/locations simple. More locations do not make a better film. Focus on telling the story. Simple is always better in a short film.
Limit your dialogue to only what is absolutely necessary.
Set relatable "urgency" early. What does your protagonist want/need? Is this CLEAR to the audience?
Everyone wants/needs something. If a character in your film doesn't want anything or doesn't help someone reach their goal, then they are not a character.
Increase the urgency/need as each failure happens
Keep it real
Steps to complete:
Concept (should be able to describe in 1 or at most 2 sentences)
Script Treatment (10 lines)
Animatic (if creating animation)
Final edit!