Hm....I usually have my mouth shut for most of the time
maybe do something to remind yourself not to speak so easily? Like if there's a funny situation and it's NOT a good thing to laugh about, I pinch my neck to stop myself from laughing. Pinching my arm does not work for me, since it's does not hurt a lot.
What I'm trying to say is try something that will stop/remind you not to speak your thoughts before processing