Tweeting to get better at blogging is a backwards way to approach the problem. If you want to blog well, you should blog until you can blog well.

I don't know about that. A big part of what holds me back from blogging (and I suspect others as well) is stage fright about putting my ideas out in public. Tweeting is a low friction way to get over that.

I would also add becoming a more active commenter as another way to get in the habit of writing in public (something I've been working on lately).