When I noticed this sort of thing in myself (I don't remember exactly when, but probably in my teens), I started intentionally pausing and rehearsing what I was about to say before saying it, in most situations. This might or might not have made me less of a liar, but it sure made me say less, because after vetting what I'm about to say, it's often the case that I don't feel the need to actually say it. Most things I would say in person don't seem worth saying once I've reviewed them for a bit.