To develop a plot, you need to find a good conflict. You can focus on finding impossible odds that your characters have to face to get what they want, their dramatic need. Think of something that you want, and think of OBSTACLES, TESTS that you have to go through.
One very common obstacle that has worked and still works is BETRAYAL. Develop a relationship and destroy it with betrayal, find a reason for it. Make it a good one.
If you are afraid of falling into a cliché, don’t be. You won’t. It all depends on how you approach the story, how you unfold the facts. Find your style. Quentin Tarantino uses a lot of clichéd elements in his movies, and he gets away with it. He is a master of this.
Personally, this is how I find ideas for my stories, I create THE BIGGEST FEAR, and then I imagine myself facing it. If I were afraid of heights, then the climax would be jumping from a cliff to the ocean in order to save whoever needs to be saved, or to chase the villain who needs to be stopped. But I imagine a BIG MOMENT, BIGGER THAN THESE LETTERS! Because is the biggest fear. Or if it’s a tragedy, when I’m about to triumph, something gets in the way and destroys me (emotionally, socially or physically). But I imagine facing the odds. That’s how I can make it believable.
After this, you have to be able to answer: What is your story about? Is it about finding the traitor? Is it about escaping impossible odds? (Maybe powerful people are after a computer genius, or a regular guy wants to save his people). Is it about facing her own fears for a greater good? Is it about struggling to get power, from being poor to becoming the king? (The main character can be the hero, or it can be the villain, like in Scarface).