I stumbled on this post by Chuck Wendig via a twitter recommendation (that's pretty much where I find all my industry-relevant news these days, to be honest). It's a great article of 25 things to know about characters. I've found characterisation one of my weakest points, which is painful because it's characters more than scenes or events that we fall in love with as readers. I thought these tips were pretty much spot on, and although none of them may individually give you an a-ha! moment, the list as a whole is a worthwhile bookmark for the 'writing' folder in your browser. It won't hurt to check it out once in a while to put your thoughts on characterisation back on the right track.
Read the article here: http://terribleminds.com/ramble/2011/06/07/25-things-you-should-know-about-character/
PS: You will notice another two links to '25 things about <interesting writing topic>' at the top of Chuck's article. As an extra-curricular exercise, do check them out, they are worth your time.