Reading about them in last weekend's Grauniad food supplement, it occurred to me that I've managed to pass my half-century without ever having a Martini - or even knowing what one is. Apparently it's a mixture of (mostly) gin and (some) vermouth (whatever that is).
Pop round to your local Waitrose and find a bottle labelled "Noilly Prat" and a bottle labelled "Bombay Sapphire". That's the Vermouth and the Gin. Also buy a martini glass - a conical glass on a stem.
Put the glass in the fridge and the gin in the freezer, until both are cold. If the gin freezes solid then it's too weak - you need a good 40%+ gin.
Pour a small amount of the Noilly Prat in the cold martini glass, swirl it around the glass so the whole thing is coated, then chuck it away (or else drink it - it's quite a decent drink on its own). Then pour as much gin as you fancy into the glass, and add a twist of lemon peel.
That's a martini, swirled rather than shaken or stirred.
Bombay Sapphire is one of the more neutral gins - Hendricks will give you more aromatics, Gordons is a slug of juniper and not a lot else, and the more expensive gins are more complex. You can also top with lime or an olive, or indeed other things.
Some people will claim that you can make a martini with vodka, or add fruit, or coffee. They're wrong. Some of them are decent drinks, but they're not a martini.