The easiest way I find to write is just to START WRITING.
I know they say to outline characters and whatnot beforehand, but honestly I get so bored doing this I rarely do. When I write stories for my college classes I just start writing and edit as I go. I will sometimes make an outline after the story has already been started and I may even ditch the whole thing and start with something else that pops into my head.
But there's no reason to think there's rules for writing something. Just start writing and change things as they come to you. You will rarely come up with things just sitting there.
Just starting to write (even if it's stupid little stories that don't seem to go anywhere) will help your mind start thinking. Characters will come to you and plots will start to form.
That's how I do it anyway
. I have no doubt I could write a whole book this way, I just choose not to because I don't have any interest in it (which I've been told is a shame because I'm actually very good at it). I tend to get nearly 100% on my writing assignments (I only lose points for grammatical errors that I overlook sometimes), but I just have no interest in writing anymore. I used to do it just in my free time, but oddly enough I prefer mathematics over writing now
BTW have you thought about taking any college courses on creative writing, just for the heck of it? The professors could greatly help you get started on learning to write, correct grammar, and how to make a story flow. I found my classes to be a great help on how to make my writing look more professional even though I was pretty good at it in the first place. You don't really realize how many things you could make look better, even if they seem fine in the first place, just by phrasing things different and whatnot, until you have a professional writer point that kind of stuff out to you.