The thing is substitution. To not to stammer, we tend to substitute the word on which we stammer with the ones on which we don't. Actually I've been trying it from past 3 days and have been successful. Don't know whether it will last though. I tend to stammer on the word H, so substituting H with a vowel did help me. TIL thing which worked for one may not work for the other in this condition. But still, it may come in handy for someone on the sub, who knows.