What i would do (and this is only my opinion here so if it sounds unworkable to you, please don't listen to it) is start writing on the story you like the most from all the stories you have in your head.
For example, take a Sunday or any other day and just sit down and keep on writing. Don't read the first chapters back yet. Just try and get as much of the story on paper/laptop/pc/typewriter (which ever you use) as possible.
Later you can work on reading the chapters back and editing them.
I have found myself readibg back chapters way too much, editing them and then having to read everything through to make sure those changes were made everywhere in the book (when it's a name or something else significant to the story)
Try to commit to a storyline that you are happy with.
You always have the option of writing multiple stories at once if you prefer and eventually you will most likely start committing to one of them the most.
So sit down and write and make sure you write for a while, commit to a storyline and write as much about it as you can and as far into the story as you can.
The detailwork you can do later. Try to commit to one for now.
If then you still want to work on other stories as well....simply start writing a new one.
I hope this was helpfull.