The Science of of Good Cooking by Cook's Illustrated is good resource for understanding what happens when you boil something, etc.
There's a ton of technique books out there, but I really like Michael Ruhlman's Twenty because it balances explaining the basic concepts and showing applications.
The Flavor Bible and the Flavor Thesaurus will help you build up an intuition for flavors.
You've probably seen or heard of all of these before, but these are my latest purchases, ready to be right at home in the new home bar I'm building...
Death & Co. - modern classic cocktails
The Dead Rabbit drinks manual
The Craft of the cocktail
The flavour bible
The Flavor Bible is a great reference for understanding flavor combinations, especially for ingredients you are less familiar with.
But it's no substitute for just eating. Eat new and different things and develop your palate. Pay attention to each new food (and ones you've had you may over look) you have - the smell, the temperature, texture, and taste. These are the things you will try to replicate.
Don't be afraid of ruining what you cook! Every good cook has failed hundreds of times and has taken lessons from that. Start with a recipe you like now and want to know how to make on your own. Mess it up. See what you learn and get better at it. Most recipes use multiple techniques so you'll be able to apply what you learn from one dish to another.