Mixing a Highball

Since most of your drinks are highballs: Scotch and Water, Vodka and OJ, Rum and Coke, Gin and Tonic or that occational Long Island Ice Tea, you better set up your private bar inside where it's warm. Be sure to use the correct glass for the concoction. With a highball, use a highball glass etc. There will be room for about 5 ozs of liquid along with your ice.
With your highball glass and ice firmly in hand, pour one and a half ounces of liquor into the glass.

Measuring the quantity with a jigger or 1.5 oz shot glass 

After pouring the alcohol, add the mixer to the drink. The mixer will usually be a carbonated drink but may be orange juice, water, or just about anything else.  If the base is carbonated, then the drink is done - the bubbles will mix the drink for you.  Indeed, mixing a carbonated drink will reduce the bubbles. If the mixer is not carbonated, it's your responsibility to either stir the drink with your bar spoon or to add a straw or stirrer to the drink for the drinker to use.

All that remains is the addition of the garnish.  Most highballs won't call for one, but you should feel welcome to add cherries to sweet drinks or lemon or lime peels to drinks with a citrus base.