Well, like others have said, just go for it. I've been suffering with writer's block recently, before I put it off for exams, but I finally started writing down some notes, and now I have a much clearer idea of what to do when I come back.
I'm not sure if this is good practice or not, but I try to work from chapter to chapter, having a clear idea of what to do with that chapter, and not thinking about anything else until it's done. Once that's done, I look at vague notes I made for the next chapter and add to them until I have a picture for the chapter, eventually repeating the process.
Unless you want to write in a stream of consciousness style (which I've never tried).
That's how I managed with my short story/long fanfic for the first seven or so chapters, before I hit a chapter in the middle which I had absolutely no idea how to write my way out of, which is when I took up the note-taking. So in my experience, writing from your consciousness only works for the beginning of the story.
It's when you hit the less well-defined 'filler' chapters in the middle that everything starts to fall apart.
Eventually I managed to work my way through that, and finish it, only to lose all of my work through a USB stick malfunction (no backups, I know) and got stuck right back at the horrible chapter in the middle.
I wanted to try and re-write it, but I got stuck, so I moved onto the next one, and now I've hit a wall in that one, I'm going to try and refinish the first one.
Once that lot's done, I plan to write a proper novel, but given my speed of writing, that could be many years down the line.