Well, pick an event (say, boy meets girl), make the circumstances unusual (say, boy has strange past), and then just follow the characters. That's how I write, I let the characters do the plot for me.
I could also advise drawing a plan out of the story, start to finish. I've just done that with my current project, and it's helped enormously.
i'm working on really focusing on plot right now too, and it's difficult. I usually start with a thought of something that should happen, and then i let the characters lead me and i write what i feel is appropriate. sometimes planning makes things boring.
I personally like the domino effect sort of plot in which one thing leads to another. And everything is interconnected and there's a big reveal at the end. This is the kind of plot I like to write.
However, plots I like to read differ very much. I never judge a book based upon its plot alone. I like to factor in the characters and the writing style to go with it. And that's the only way I judge a plot is if the other variables are justly so. Pacing is always a very important thing in a plot. You never want your book to be too slow, or too fast. And it's tricky getting the right balance.
I'd choose the plot that a group of related people(family, friends, whatever) who go out for a night. Before that night, they, or some persons in their environment, commited a crime. It is still a secret, and they should talk aout that ,but they don't. Eventually it becomes clear that there is more going on that the crime. Maybe they all have a different past, and they are not who they say they are. That's what I would do:)