according to my speech therapist, blocking, repeating several words or sentences, facial tension etc. are behaviors that we adopt unconsciously when we want to stop ourselves from stuttering (for example: we block when we try to force a sound to come out). So the best thing to do is to accept stuttering and repeat, even if it seems unnatural or embarrassing. However, if it's too difficult to let yourself stutter (I still have trouble with that for example) we can always use other and more useful techniques, like Erasm that I saw in another comment, or simply slow down to better organize our speech (even if it is sometimes complicated to think about it or annoying to do, it remains one of the best methods) . I hope it helps!