Gear
Technique
Although the techniques of a chef are many, the techniques of a bartender are few, which is all the more reason to master them.
Ice - Is ice equipment, or is it an ingredient? Perhaps it is both. It is a common element between the majority of your drinks, and you should pay attention to its shape, clarity, and flavor. Ice that sits in a freezer for too long develops unpleasant aromas. Ice which is impure becomes cloudy, and ice with a suboptimal shape will melt too quickly. The best ice is cubical or spherical, clear as glass, and fresh. Always pursue excellence in your ice.
Dilution - It sounds simple, and it is. Still, there are considerations when stirring a drink. The first question is, what is the right technique to mix a drink? The answer depends on the ingredients.
Drinks that contain fresh juices or any significant fat content will benefit from aeration, which shaking provides.
Stirring is appropriate for drinks that contain only spirits, bitters, and syrups.
Stirring and shaking are primarily about dilution. You can incorporate the ingredients in a drink with just a little agitation, but undiluted drinks usually aren't very good.
By volume, water makes up the largest single component of your drink, so it is worth it to pay attention.
Proper dilution can make bad spirits palatable, and good spirits divine.
Regardless of your method, you should expect your drink to gain two to three ounces of water when you mix it. The proof of your drink, pre-mix, is probably around 80 or 90, and it should drop down to somewhere between 40 and 50.
This is desirable, because it will make even a low quality spirit taste "smooth", and will help some of the subtler flavors come out.
Stirring - The first method for diluting a drink is stirring. Stirring should be done gently and quietly. The goal of shaking is to aerate and froth a drink; the goal of stirring is to leave it as flat as possible. A martini or a manhattan should be perfectly clear and smooth. Air bubbles will disrupt both appearance and texture.A stirred drink should be soft, like velvet.To stir, place the back of your spoon on the outside of your mixing vessel (the larger half of your cocktail shaker is adequate), and gently revolve it around the outside. Try not to make any noise as you move through the ice. Depending on the size and temperature of your ice, you will probably want to stir for about thirty seconds. It takes some practice to develop an intuition for when a drink is "done".
The act of pouring the drink from shaker to glass is another opportunity to aerate. Therefore, pour as gently as you stir. It is generally not necessary to use a fine-mesh strainer with stirred drinks, as there should be no small particles to remove.
Shaking - Shaking is arguably simpler than stirring. Pour the drink over ice, clamp down you shaker, and shake. Shaking is the most theatrical part of preparing a mixed drink, and it's worth investing in your optics. If you want an example of shaking perfection, look no further than Kazuo Uyeda, who does at least three things against my advice, (cobbler shaker, free-pouring, no fine-mesh strainer), but he's Kazuo Uyeda, he comes from an older tradition, and he can do as he likes.It is a great idea to follow his theatrics, but it is not so great to follow his pouring technique. Strain your drink, and don't leave me with a bunch of pulp and ice floating on top.
Tasting -To taste your drink, hold up your hand, palm facing down, and scrunch up your thumb to create a small divot between your thumb and your wrist. Using your barspoon, ladle a taste of your drink into the divot and then slurp it from your hand. It may sound a bit boorish, but it's better than drinking out of your barspoon, and it will make it look like you know what you're doing.
Tasting is the critical, and under-appreciated, technique of the mixologist. I suggest tasting your drink both before and after you mix it, using the technique above. This will help you verify that your pre-mix ratios are good, and your dilution and chill are good.
You should even go further: to truly understand your drinks, you should taste each component separately (do it on your own time, not when your guests are waiting) in order to appreciate the contribution that each piece is making. If an ingredient is not coming through in the final product, cut it, or beef it up. Don't endure useless ingredients.
Serving - Drinks that are not lengthened with carbonation can be served either Up or On the Rocks. To serve a drink up, you will select a cocktail glass (also called a Martini glass by the plebs), and pour the drink into it. A drink that is served up should never contain ice. To serve a drink on the rocks, you should, prior to mixing, have a tumbler (or "rocks glass") ready and full of fresh ice. Do not use the ice from your shake as the ice in your drink. It has already been cracked and partly melted.
After mixing the drink, pour it over the fresh ice in your tumbler. It is important that the tumbler be full to capacity with ice. A small amount of ice will melt quickly, but a large amount will keep itself cold, and melt much more slowly, helping you to retain optimal dilution.
Glossary
Before we get any further, here are a few key terms.
Base spirit - Any of vodka, whiskey, tequila, gin, rum, brandy, calvados, pisco, cachaça, shochu, soju, baiju, or any other relatively unsweetened spirit. On occasion, any spirit can fill in as a base, but generally we mean the above.
Souring agent - an acidic liquid, usually lemon or lime juice, but maybe yoghurt, cranberry, vinegar, verjus, or a powdered acid.
Modifier - A small amount of a flavorful liquid, usually a liqueur or a syrup
Bitters - Concentrated flavor tinctures that add complexity and depth. Made by steeping bitter herbs in strong alcohol.
Simple Syrup - A mixture of 1:1 sugar and water (by volume), heated just enough to melt the sugar and clarify the liquid.
Lengthen - To add a large volume of a mild liquid to a drink, to make it weaker and extend the time it takes to drink it. Most commonly carbonated water or tea.