Patrick has done a much better job at this than me and I wholly second this, please read his guide first, then skim mine to see if there is anything useful in it. When I wrote mine Patrick's did not exist yet, if it had then I would have happily skipped writing it.

I was coming here to post that same link. It's much longer, but contains many more specific situational examples, and more comprehensive advice.

Thanks for posting this, it's in the same vein as the original link but far more thorough.