I've sometimes been in the habit of talking into my phone, which conveniently removes the social stigma as long as no one is close enough to hear what you're saying. Taking walks helps. You can either record yourself or not—I find that talking into an inert phone feels awkward while recording myself makes me feel a little self-conscious. I never did find a method I was completely comfortable with, which might be why I don't do it anymore.

Anyway, I'm generally a fan of self-talk / private speech. I think it's a good way to put your thoughts through a BS detector, or at least so goes my theory: since you're hearing the words aloud you interpret the message as if someone else were saying it and so you hold it to a higher standard.