Ah... we have the same problem! :))

Out of the 8 (so far) stories I have, I've only finished one. :)) I think our problem isn't so much starting, but with finishing? IDK hahaha.

It's really hard to be constantly inspired, and sometimes you get inspired with a new story idea in the middle of writing one...

For the only one I finished, I think I kind of just wanted it to end. Like, when you reach a certain chapter, you just know what's gonna happen in the end... I liked living in that story's world but I guess I wanted to move on, and since it was my very 1st fic, I really pushed to give it a nice ending. :)

I don't really know what advice to give since I'm the same way hahaha but sometimes it helps me to re-read the whole story, or at least a couple of the latest chapters, from time to time, to get the feeling of the story once more. I find that I get inspired after reading other fics or books, sometimes watching movies or series... Then I do the re-read, type whatever comes out (sometimes it's not for the next chapter, like, if I'm working on chapter 10 then I get an idea for a scene that can't happen yet, say, something suitable for Chapter 11 or 12, I'd just write everything down) and keep it up as long as the inspiration is there, because when it's gone, it's just hard to get it back...

As for your question, like Snowflake21, I do put up forewords easily when an idea strikes me. :) I can also churn out the first chapter (or the first two, if I were THAT inspired and had time lol) the same day. I don't really have plans yet for the entire thing, just the first few chapters and a general idea of what I want to happen later... The problem is just to continue after getting stuck or getting busy...

*sorry this is so long but I hope it helped a bit*

hahah I know exactly how you feel :-P
I can have an idea in mind, quickly put up a foreword, (which is probably okay most of the times) and then just leave it for a couple of months, put up another foreword and leave that too for a while :-P But I do always come back to them at some point though :p
It's hard to explain how to tell you how to actually start up a story. Just have an idea in mind, and go on from there? It's okay to not always have a plot in mind for the whole story from the beginning, like for me I can put up a foreword but have no idea yet what i will write in the first chapter. You can kind of make it up along the way but you should have a general idea in mind of where you want it to go. Just so you know, it's okay to leave forewords/stories for a while, some I haven't updated in a LONG time because I simply didn't have inspritation for it but then one day I do and I just continue the story, don't feel pressured to update if you simply have no inspiration yet ^^Sorry if this i'm not good at giving advice XD