Read aloud regularly.
The benefits of reading aloud are numerous. I was able to access whether my children were reading word-for-word or if they were reading phrases, how much they understood what they were reading (reading comprehension), and how confident they were just by listening to them read aloud. It also afforded an opportunity to discuss the things we read and to correct mispronounced vocabulary. They all grew in reading confidence and would volunteer to read when asked in public settings. When reading literature they added inflection and accents. They had fun with the activity once it became routine.
The confidence that your children gain by reading aloud will enable them to give speeches, presentations, and introductions naturally and unaffectedly.
My final word on the topic – read aloud with them!