I'm no Obi-Wan of fiction writing, but I'd be more than happy to share a few tips.
Usually when I brainstorm ideas for my story, I like to picture random scenes in my head that I intend to write at some point. They aren't always in chronological order but if I find myself wanting an event to occur later in the story (a car crash, for example), I open a word file and type the event, the chapter number and the characters involved. Something like this:
CHAPTER 6 - (Character) drives off a cliff
That's just to give you an idea where your story may be heading. Nothing has to be set in stone, though. To connect scenes together, I personally like drawing web diagrams on a notepad (because I pace around a lot when I brainstorm). I find that this helps me see the bigger picture and allows me to plan ahead without killing my muse. Here's an example (do not take it seriously):
Angel is a vampire--->Xander is in love with Angel--->Angel gets smacked by an old lady with a rolling pin--->Angel gets pretty banged up--->Xander shows up at Angel's place with flowers--->Angel attempts to bite Xander--->Xander drives off in terror--->Old lady crosses the road and causes Xander to swerve to the left and drive off a cliff--->THE END
Now obviously that was just a fake plot. It makes absolutely no sense but you get the idea, right? If we hadn't mentioned (or at least alluded to) the fact that Angel was a vampire in the beginning, it wouldn't have made sense for him to want to eat Xander after getting smacked around by the old lady.
Also, it's good to have at least a vague idea of the ending in mind. If, let's say, you decide to end a story with a lesbian taking a pregnancy test and finding out she's pregnant, there has to be a point in the story where she's done something to make the pregnancy test scene believable. Is she a surrogate? Has she been with a man at least once? Has she and her partner planned to get artificially inseminated? This way you'd know what events should occur for the story to progress logically and realistically. She can't get pregnant without having done any of the above. Unless, of course, you're writing the Bible.
I personally use plot outlines because they help me stay organized but if it's not your thing, remember that many authors get by without it. So whichever works for you.
Good luck and have fun planning!