Our breathing, throats, and jaws all play an important role in how we sound. But clear diction is also governed by our lips, teeth, and tongue. Lips should hit against each other on the "P," "B," "M," "W," and "WH" sounds.
Practice: Create these sounds and the vowels in between by saying "PAPA," "MAMA," and "WAWA." Make sure your lips hit each other and build your speed. Try longer phrases, increasing your speed as you go along: "We have rubber baby buggy bumpers." "Peter Prangle picked pickly prangly pears."
Keep practicing until you have an open throat, an active lower jaw, strong lip muscles, and a flexible tongue that can trip lightly over tongue twisters.