I have two methods that aren't 100% reliable but they often work: 1. The classic "umm, uhh, umm" before starting the sentence helps the words flow out by kind of piggybacking off the umms and ahhs. 2. I picture the word I want to say. Like if the word is "today" I will imagine the written word "today" and if the word is a more tangible physical object, like "table", I will imagine a table and then start speaking. Try giving method 2 a go. I can't remember if I read about it somewhere years ago or if my childhood speech therapist recommend it but I've been doing it since, it would be interesting to see if it helps other people.