If anyone is interested in getting into cocktails I really can't recommend Cocktails with Suderman enough. The early posts are free and go into the theory of how cocktails are structured and why they work. Once you start to understand the structure of the major cocktails it makes it a lot easier to understand how you can play with the ingredients and make something new.

For instance, tons of cocktails fall into the "sour" category. They usually have proportions of 2:1:1 or 3:1:1 of a liquor, a sour, and a syrup. If you have rum, lime juice, and simple syrup it's a daiquiri. Swap out the lime juice for lemon juice and the rum for whiskey and you get a whiskey sour. Swap out the simple syrup for honey syrup and you get a Gold Rush. Use tequila, lime juice, and a blend of agave syrup and Cointreau and you have a margarita. Gin, lime, and simple syrup is a gimlet. And so on.

Also, as others have mentioned, the quality of the ingredients and the brands often matter a lot. A Manhattan calls for whiskey, sweet vermouth, and bitters, but the choice of whiskey and vermouth makes a big difference in the character of the drink. (And if you are using old vermouth that has been sitting out on the counter for a few years, or making a drink with bottled lime juice, it's just not going to turn out all that good.)

https://cocktailswithsuderman.substack.com/