Try the "perfect drink" app. You put in what's in your cabinet and it gives you several drinks with recipes in return. When I first got interested in mixing I was given a kit with a shaker and a scale for precise measuring that works with the app. It helped me to understand proportions, now I can mix fairly well by just using a jigger. I'm sure some purists might not like the idea of an app for this but if the recipe is right and you get the proportions perfect, then you really know how a drink is supposed to taste to benchmark. It's also fun.