Hey! I didn't know you could reach the 8th octave saying "Alphabet"!

[edit] Steps

Get past the age of puberty. Everything's so weird and embarrassing, with the extra hair growth and the voice changes. Give it a couple of years, it'll peter out eventually. Your voice will even out too!
Relax. Your voice naturally gets higher when you are tense. If you are speaking before a crowd, try to relax and take deep breaths. Try not to be nervous, this will cause involuntary spasms in your voicebox, causing the pitch to fluctuate. Calm down.
Give your voice a rest. Try not to scream. Bellow (from the hips) if you have to, but don't scream (or squeal). Get a microphone or cup your hands.
If you are a screamer, take it easy on the icy cold water. Drink lukewarm water instead. Imagine getting doused with ice water after a workout. You involuntary tense up, no matter how awesome it feels.
Drink water if you will be talking for a while. There's a reason David Letterman has a mug on his desk. This will lubricate the throat, which reduces stress on the chords.
Try making a hot water and honey drink to calm the vocals.
Related: Don't try to talk or sing after eating a chocolate bar or you will end up with a scratchy, gargle-y throat.
Use your own voice. Don't try to butch up, unless you are comfortable in that voice. When you lower your register consciously, that gives you a greater range for your pitch fluctuations. If you don't like your voice, practice modifying it before engaging a crowd. Don't whip out the Barry White when you're actually a Gilbert Gottfried.