Ideas are all around us. I'm sure you have at least a dozen ideas floating in your head. Maybe more. Not all of these will become stories and not all will be right for you. So before we begin to look at plots in depth let's explore which idea works best. Then we'll get into plot.
Remember this, a plot is a plan or a roadmap for characters on their way to a goal. There are scenes but they must be significant and have an impact on the characters as they aim for their goal.
1. Is it your story to tell? There are some stories I could never write and there are probably some you can't. For me, horror is one, another westerns and a third science fiction. Not that I don't enjoy reading them, maybe not horror since I'm a chicken. So when an idea suddenly appears think if it's one you could write. Make a list of those type of stories that aren't for you. Maybe you like mysteries but police procedure is your kind instead of cozies or hard-boiled detectives.
2. Is the too personal to engage a reader? Some experiences are too close to you or there are some you feel like preaching about. These will turn a reader off. While our own experiences are fodder for fiction, it must be remembered that the characters are the ones experiencing the event of what ever you're writing about. While there is some of you in the character, the character isn't you.
3. Can the idea go somewhere? Maybe after twenty or thirty pages you start spinning your wheels and the story stops flat. Might mean taking a second look at where the story is heading and seeing where you stalled.
4. What's at stake? What's at stake for the character? Are the protagonists equal? With unequal characters there's no real conflict. If your villain or villainess is so evil the hero or heroine stands no chance, the idea won't work. If the hero or heroine is so plum perfect and strong and the bad guy or girl weak does what's at stake really matter.
So when an idea pops into your head, look at each of these areas and if all are a go, then run to your computer and begin to tell your story.