First off, Practice many times before if you have the time. If you have to do it kind of on the fly, i always start with a joke which calms me down and boosts my confidence. I feel when I am more confident is when I can speak without a stutter. When I have anxiety about my stutter im always thinking of the next vowel that will come up which will either cause me to prolong the word or will cause me to pause because of the blockage. Then I have seconds to come up with another word to replace the word I cannot say. Either way, PRACTICE and CONFIDENCE is key. If I am informed enough and confident enough about whatever I am presenting, when I speak it will be with conviction and certainty. Rather than having to come up with words on the fly causing uncertainty and anxiety.