Nick - do what I do: start yodeling.
Anybody can yodel; it's controlling it that takes a bit of practice.

Seriously, warm up your voice with vocal exercises first.
I like to chew a little candied ginger to get the phlegm off my vocal cords, and then vocalize.

Occasionally I'll have a little break in the voice, and I'll get a laugh by saying "Puberty! At last!"

Seamus