There are a few, essential tools a good bartender keeps at hand. First, the Jigger. A Jigger is an hourglass shaped mechanism used for measuring the proper amounts of liquid for your cocktail recipe. A jigger is comprised of two parts, the larger end is the jigger (measures 1.5 ounces of liquid) and the smaller end in the pony (measures 1 ounce of liquid). The simple, classic, stainless steel variety are recommended. I recommend this jigger for your application: Once you get more practice at the measurement, you might even be able to eyeball it, and not even need a jigger. Many experienced bartenders can eyeball the measurements with ease, but it comes with practice!
If you don't have the beaker, I recommend this one. Be sure to select the 28 oz version.
An optional piece to a bartender's arsenal, is the muddler. A muddler in a cylinder-like shaped device with a rounded end, used to pulverize ingredients, such as fruits and herbs, releasing the flavors into your cocktail or food. A wooden muddler is best, as it naturally has the best texture to create the appropriate abrasion to the ingredients for your cocktail. You may have one already in your collection of kitchen gadgets. If so, feel free to be resourceful and use it. Don't have one? I got you covered. Try this popular muddler.
Rest assured that quality bar ware doesn't have the break the bank. In fact, the aforementioned tools can be had for less than twenty dollars!
Now that you have your hardware in line, how does one use it? The procedure is amazingly simple. First thing's first, you need ice! Put a handful or two ice into the metal beaker of the Boston shaker. Use the jigger to pour the appropriate measurements into the metal shaker with ice. Take your glass or plastic pint glass, and invert it into the metal shaker. Give the pint glass a medium whack into the metal shaker to create a vacuum. Hold the shaker on both ends and shake horizontally. When the cocktail is combined, give the metal part of the shaker a gentle tap against the ledge of your counter or bar to release the vacuum, or you can give the metal shaker a little squeeze and twist, whichever is easier for you. Strain the drink into a prepared glass by holding the shaker and pint glass edge to edge in a wide V shape over the prepared cocktail glass. Just check out the picture of the bartender above for a visual aid. The prepared glass can either be a chilled glass of your choice, or a glass of your choice with fresh ice in it (depending on the type of cocktail you're making). If you plan on using your muddler for a drink, such as a mojito, you can mash the mint and sugar in a glass you will use to serve your cocktail, add remaining ingredients and stir with a long teaspoon or cocktail stirrer.
Simple tools and fundamental techniques make for a skilled bartender. Practice these tips at home before your party and you'll be a hit with your friends and family.