@the other dave, those are excellent for singing and, when actively used, social situations, but there are other techniques which are more passive. The Khargyraa, Tuvan, Diaphragm Breathing, Nasal Passage Opening, and some more general speech techniques including speaking slowly, pausing often, knowing when to gesture, all of these contribute more effectively to your impression than the techniques you mention, which fade as soon as you get caught in the moment.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.