We fans of the classic cocktail love our strong, spirit-driven drinks, but not everyone enjoys the taste of alcohol and many people don't or don't want to drink as much of it or any at all.
A good host - whether at home or in a professional setting - should be able to provide the same pleasant experience of the perfect beverage for a guest anywhere along the spectrum from "straight up, no chaser" to teetotaler.
Jeff Hollinger wrote about this beautifully in his book The Art of the Bar in the short sidebar on serving kids at events (starting on page 60).
Look back at your Jerry Thomas and Harry Johnson bartenders' guides of the 19th century and remind yourself how much coverage there is of the drinking world beyond the booze. Start making yourself something special in contexts where you're thirsty and an alcohol-centric drink isn't appropriate. Build your repertoire and explore new ingredients. What juices go well with which garnishes? Sweet or spicy is easy, but what to make for that Manhattan and Martini loving friend when he's taking a break from the booze? Try building up from your mixers, garnishes and other non-alcoholic ingredients as well as working down from spiritous cocktails to create temperate versions.
You'll find there are good resources out there for non-alcoholic drinks - the best cocktail manuals always include a section on them - and helpful new books from a cocktailian's perspective such as Natalie Bovis-Nelsen's Preggatinis: Mixology for the Mom-to-Be. Just as when you first began learning cocktail standbys, teach yourself a half-dozen non-alcoholic or "virgin" drinks covering a spectrum of tastes and available ingredients which you can use to make your guests feel well cared for, regardless of their alcohol intake.
Next, push yourself to a higher skill level by filling in the middle ground with a half-dozen shims - remember the shim? - which you learn by heart, and bring these low-alcohol cocktails into play whenever a little less kick is appropriate: between rounds on a long evening, as the first round while the appetizers have only just begun to circulate and people have empty stomachs, as the designated driver's one drink before switching to non-alcoholic choices, on a second social evening in a row when the first turned into a bender, or just to keep yourself level any time extra balance is needed.
Mix it up for everyone!