The professional bartender is agile behind the bar; expedites cocktails, beer and wine efficiently and accurately with courtesy; and cleans up spills, napkins and squeezed-out fruit off the bar as they appear. He can tell a joke on the fly, commands the bar with authority; makes eye contact; and knows who has had too many drinks and who needs another. But like most things in life, preparation above all else makes that possible. The primary requirement of any bar is that it be efficiently set up and fully stocked.
Behind most bars, you will be centered around your speed well, which is the speed rack in your immediate reaching distance containing the cheaper, "well" brand liquors and the soda and juice "gun." All liquor bottles should have a speed pour-top inserted by uncapping the bottle and pushing the pour top all the way in. Pour tops regulate the flow of alcohol from the bottle, making pouring liquor much neater. Bottles should be arranged from right to left: vodka, gin, rum, tequila, triple sec, whiskey, scotch, lime juices and grenadine. This is a general rule as to which liquors are used most frequently. This may vary from bar to bar, but know there is an established order and usually a good reason for that order.
You will want an appropriate amount of cut fruit to match the type of event you are working or hosting, and it's never a bad idea to cut what you think might be too much fruit. Try to know what type of crowd you are serving; this may give you an idea as to which types of cocktails they drink and which type of fruit to have most of. Always have some of every type of fruit on hand, as you may have an uncommon order. Also, make sure you have enough mixers: juice, soda, sour mix and bloody Mary mix.
Once you have your liquors, fruit and mixers all set and in order, you need to make sure you have support material, such as a good amount of bar rags for soaking spills off your bar. Dirty bars equal poor bartenders. Have plenty of beverage napkins on hand and serve every drink with one. Have two shaker sets in case one is dirty and you need the extra just make the drink at hand. Also, have at least one strainer on hand. You will use it for something.
Open a few of the wine bottles you will be serving ahead of time. Opening them on the fly takes time and can be inconvenient when 10 other people just want a beer from the tap. Make sure if you have kegs that are not empty or close to it. Changing a keg takes even more time, and it can earn you some frustrated customers. Be sure to stock your bottled beer, and make sure the things you need are an arm's length away or no more than a few steps.
At the very least know the basic drinks and terms. You should know what a martini and Manhattan are, and know what "on the rocks," "up," "dry" and "neat" mean. You should know that "captain and Coke" means Captain Morgan's Spiced Rum and Coca-Cola. If you don't know these terms off the top of your head, with five orders backlogged in your mind and more being given to you, your patrons might see it as you stumble over the service you give.