It's called Noplotitis. Ugh! I can never figure out a plot for my stories, I guess it's not that hard, but it is for me. I just get a basic vague idea for a story and then go after it, get really bad writers block and can't go on. I never ever know how a story's going to end. Any tips that help you? please? i'll be your best friend.
Yeah, it is kinda hard. This may sound crazy, but I look at a few different things around me. For example, right now I've got a DVD of Frasier on my desk and a book by Michio Kaku called Parallel Worlds and a plasma ball. Try to find a way to connect the three, and you might have a completely insane story! A group of funny people in an apartment that accidentally create a wormhole to another world because they dropped a plasma ball in a bathtub! It's crazy! Or think about a character in your story, then look at an object or an idea in real life. Connect the two and you might discover something!
He's right- just take a few bizarre things and build. 'What If' questions are good, too, especially when derived from the aforementioned scenario. For example, I once Googled the word 'apocalypse', and wondered what would happen if I actually got a helpful answer. That resulted in my starting the only novel I've ever felt I could actually finish.
If you have a basic starting situation, try building up your characters. Whem your characters become interesting individuals whom you feel you know well enough, you will have a good notion of how they will react to the situation. As soon as characters begin interacting with the scene, the situation begins to change, and so do the characters. That can also drive you to introduce additional characters, and the plot grows. It's a starting point, anyway.
I usually have at least one character in my head before a plot comes. If you fix in on a character that you like and that you can make real then plenty of story ideas will come to you. I have one character in my head at the moment and am juggling a few plots around in my head about her. I don't know how things will turn out but I get better plot ideas when I have characters that are quite fully formed.