I've been more of a traditionalist when it comes to my Old Fashioneds. There's two techniques that are different enough to produce divergent drinks, but similar enough that it merits highlighting both. One requires a little more advanced preparation than the other...not much, but a little.
First up is David Wondrich's technique as outlined in, you guessed it, "Esquire Drinks":
In the bottom of an Old Fashioned glass, place a sugar cube, or 1/2 tsp of loose sugar. Wet it down with two or three dashes of Angostura bitters and a small splash of water or club soda. Crush/mash/muddle the mixture until the sugar dissolves as much as possible, then rotate the glass so that this syrupy goo in the bottom coats the inside.You'll notice that there's no fruit muddled in there, and really, no garnish of any kind. Wondrich points out that "F.D.R. took his with only a twist, and he led us thorough depression and war," which I think is a fair point.
Add a large ice cube (or two smallish ones) and pour in 2 1/2 oz of rye (or bourbon. BUT NOT BRANDY, YOU BLASPHEMER!) then squeeze a twist of lemon in and serve with a stirring rod.
My preferred technique, though, is one used by Jeffrey Morgenthaler, a terrific bartender out of Oregon. He uses a simple syrup in lieu of the sugar and water/club soda, and he actually does a tiny bit of muddling. But I get ahead of myself. First things first, the simple syrup. He suggests a 2:1 syrup, that is, 2 parts sugar to 1 part water. This makes for a richer, more concentrated sweetener, and one that is less likely to dilute your drink (the ice doesn't need any assistance on that front). So just mix up your syrup by adding sugar to boiling water, making as much or as little at a time as you want (I just made up a small batch with 6 ounces unbleached sugar and 3 ounces boiling water) and have it standing by. Here's Morgenthaler's method (also available in handy video form!):
In your Old Fashioned glass, combine 1/4 oz 2:1 simple syrup with two dashes of bitters. Add a section of orange peel, and gently press with your muddler. You're not pulverizing it to a paste, you're just pressing the oils out of the peel. Add two ounces of bourbon or rye (I prefer rye, but that's just me) and stir to combine. Add a few large ice cubes and stir until the glass just starts to frost or sweat, or until you just can't wait anymore.I like the elements of orange that Morgenthaler's technique brings to the drink. Wondrich's is good, don't get me wrong, but by going with the simple syrup and the orange peel, you get a great deal more flavor without any grittiness. Both are great examples of the gold standard style of cocktailcraft, however. Let the ingredients do their jobs, and you won't need to gussy it up like some sort of be-lipsticked and rouged pig, which I feel obliged to point out is pink...just like a Cosmopolitan. Oh, and it's just not kosher, either.