WHAT IS THIS BLASPHEMY!!!
I'm just kidding.
A real martini consists of gin and vermouth (either dry vermouth, sweet
vermouth or both; a dry, sweet, or perfect martini). A gin martini is never
shaken because the gin will cloud up, and give a less than appealing
presentation.
Vodka martini's are the same way, except they can be shaken (ala JamesBond)
or stirred. Either is appropriate.
Both of them can be garnished with olives (no more than three though, because
that just looks silly and audacious) or a twist of lemon.
When you're making appletinis, pomegranate martinis, etc. Use Vodka as the
base, and then add a flavored liqueur. And garnish with what seems
appropriate.
Get the basics of a good martini down (both gin and vodka), and then
experiment away! Despite my purist tendencies (i like mine either vodka or gin
with a bit of vermouth, and a few olives), the martini is a great platform to
create off of.
But I can't stress this enough: UNDERSTAND WHAT A MARTINI TRULY IS BEFORE YOU
START CREATING!!!