Technique
Shake hard with cold ice and strain as soon as the shaker is frosted. Before shaking, taste a drop of the mixture: limes vary, so a very sharp one may need a bar spoon more syrup, while a softer lime may benefit from slightly less.
A daiquiri is a family of cocktails whose main ingredients are rum, citrus juice, and sugar or other sweetener.

TonicDB editorial guide
The classic Daiquiri is simply rum, fresh lime, and sugar, which makes ingredient quality and measurement unusually visible. It should be brisk and refreshing, with neither the lime nor syrup hiding the character of the rum.
Shake hard with cold ice and strain as soon as the shaker is frosted. Before shaking, taste a drop of the mixture: limes vary, so a very sharp one may need a bar spoon more syrup, while a softer lime may benefit from slightly less.
Serve straight up in a chilled coupe or small cocktail glass. The modest serving size is intentional; a Daiquiri warms quickly, and a smaller cold glass preserves its crisp texture better than an oversized martini glass.
Bottled lime juice and casual free-pouring are the usual reasons a Daiquiri tastes flat or unbalanced. Under-shaking leaves it sharp and warm, but letting it sit on spent ice after shaking introduces too much water.
An aged rum creates a rounder drink with vanilla and barrel notes. Begin with the same 2:1:½ proportions, then reduce the syrup slightly if the rum already tastes sweet or increase it by a bar spoon if the barrel character feels too dry.
These notes explain how to execute and adapt the recipe shown above. Ingredients and serving traditions vary, so taste and adjust thoughtfully.
Contributed by @alfg