Better to speak E slowly?How?

[Squirrel_3110]

Hello! I heard from a video clip in which an English teacher said that it is very important to speak English slowly to pronounce an English sound (vowels) fully. I think it sounds to make sense, although in places I live, people often think that speaking English as quickly as possible is good. However, I am wondering how we can slow down our speech without changing intonation and rhythm. We shouldn't read word after word, should we? So how? . And another question: Can I make my voice stronger because I find English need long breath (reporters on news channels often say nonstop!) and as an English teacher, it is extremely essential to speak loudly which means a strong voice is needed.Thank you very much