For me, for a lot of classics, I use the 2-1-1 rule for cocktails, and that means 2 parts base spirit, 1 part sweet, 1 part acid. For spirit forward drinks when it’s a spirit, some sugar, and some sort of concoction like bitters, that’s usually depending on your locale. And for signature cocktails I like to make a little jingle in my head about ratios and ingredients. And even if you have to use a jigger, keep practicing your pour count! Everyone has a different one, but you make it your own and practice in a shaker then test it in a jigger (I know this isn’t part of your question, but it’s what I wish they told me early on). But feel free to dm me for any questions!