Disclaimer: I am not a good writer, but at times in my life I have tried to be. Here are a few things that help.
1)
A Copy of Strunk and White goes a long way to making you seem like you know what your doing
2)
On Writing Well helps to keep you on task and exposes you to a wide variety of ways to approach writing
3) I try to carry around a notebook for when I hear an interesting turn of phrase or situation that I think would make a good topic
4) Read - Self explanatory, but dont just read stuff you like, read something that is a "classic" but that you dislike and try to find out why it is regarded so highly