As you start to make your own liqueurs and mixers, you'll notice very different levels of sweetness compared to the mixers you buy in the liquor store. This is a good thing, as it gives you more control over the final product and it gives you the option of using additional sweeteners if you feel so inclined.
However, to sweeten a cocktail successfully, you need to have an understanding of what your options are how they will impact the final product. Below is a list of some options for sweetening your drinks and what they add to a drink. This is by no means an all inclusive list, but I've tried to hit some of the more popular options.
Simple Syrup: This is a neutral sweetener that will give your drink the hit of sweetness that it needs without any additional flavors. Sometimes a non-intrusive sweetener is the best option and in those cases, go for the simple syrup. You can whip this up at home with equal parts granulated white sugar and water.
Honey: There are so many types of honey with such nuanced flavors, therefore making it hard to make sweeping generalizations. Honey is a great natural sweetener, although it is quite thick and that consistency needs to be taken into account. I like pure wildflower honey, as it has a light floral aroma and a great clean flavor. Get out and experiment with some honeys to see which you like best.
Agave Nectar: A natural extract from the Agave plant, agave nectar is a viscous sweetener that works great, not surprisingly, in tequila cocktails. Agave nectar is great for the vegan crowd who won't eat honey, as it has similar flavors and is entirely plant based. There are different grades of agave nectar with the darker versions having slight notes of caramel.
Brown Sugar: is white sugar with the addition of molasses. That molasses can be naturally occuring during refinement, however, these days it is more often added back into granulated white sugar during refinement. The addition of molasses gives brown sugar a stronger, more distinct flavor that has hints of butterscotch.
Maple Syrup: Lately, maple syrup has become a very popular natural sweetener. It has a light sweetness and it tastes like, well, maple. Maple syrup is a nice addition to cocktails particularly in the fall (bourbon+maple syrup is a great combo).
Now go make some cocktails!