Before beginning, have the students share some tongue twisters they know and try saying them five times in a row, getting faster with each repetition.
Begin with a basic sentence to build on, especially for younger students.
e.g. Lucy likes lollipops.
Have students expand the sentence. (A good place to tie in parts of speech.)
Little Lucy likes licking lollipops.
Lazy little Lucy likes licking lemon lollipops.
Lazy little Lucy likes lying on the lawn, licking little lemon lollipops.
Lazy Luke and little Lucy like lying on the lawn, licking limey-lemon lollipops.