Hey LJonesy, don't mention the rugby,
although I could claim Welsh heritage.... Actually, you sound Welsh.... Nah, unfortunately, (in rugby terms, anyway) I'm English. Saeltari's link is great, Here's how I do it, not sure if it'll help, but you never know:
I start with a 'whatif' file, and I just keep jotting down ideas as they occur to me, so I
always have a pad with me (actually sometimes my phone notebook will do) If I don't do it at the time the muse fairy takes the idea out of my brain after 5 minutes. The more I think and write down the ideas, the more they come, so I end up with a complete mish mash of ideas that are in no semblance of order, just as they've occured to me. When the ideas slowdown I start editing all my ideas into whatever order I feel is best (usually chronologically). Then, and only then, I start musing on character pictures - what's the colour of their skin, eyes, the clothes they wear, where they went to school, their favourite music, food, their friends, their parents, their pets, their likes, dislikes and so on, ad infinitum. I will never use 90% of what I know about them, but they are so fixed in my mind that they always act in character (unless I need to jolt them out to make them do something), and I personally find that my story flows so much easier - I don't have to stop to keep thinking 'Ooh what would he do/think/say etc?'
Of course periodically an even better idea occurs to me, so I go back to my edited summary and insert it. Sometimes I have to edit my edited summary, and then edit the edited, edited.....you get the idea. The best advice I was ever given which cleared my mind when I was really struggling to write was: "Know where your story starts, and where it ends. The rest is just hard work...." ie we can all work hard, but if we don't know where to start and finish that hard work will be for nothing.
Good luck.