I want to take a quick dive into what I think makes a great non-alcoholic cocktail. First, it should have an intensity of flavor. Cocktails are not shy things and alcohol is a wonderful solvent, carrying flavors. Ergo, NA cocktails should also include bold, strong flavors.
They also need to have a certain texture. That texture comes from viscosity, how thick is the liquid (e.g. honey has a lot of viscosity, water does not). You can use a range of ingredients from fruits to grain milks to gain texture. And there are also great NA cordials, too.
For NA cocktails, you have to account for the volume of the drink generally reserved for alcohol, between 1 and 3 ounces. You can do so by increasing the ingredients or adding new ones. But making a Daiquiri by subtracting rum isn’t going to work.
Then there’s what I refer to as piquancy: the bite of alcohol. The thing that twists your face a little (or a lot). Alcohol adds heat and astringency. Ginger, peppers, bitters, vinegar do a nice job of subbing here. Especially, ginger—it’s my favorite NA cocktail ingredient.
If you can pull these together, you’ve got a great non-alcoholic cocktail. Not just the grenadine and ginger ale special suggested by @MrJustinStone (facetiously, of course). I’ll post a few examples later today.