I have friends who are partial to a cocktail but they have admitted they find the prospect rather intimating. I have recently discovered that I don't, in fact, need hundreds of bottles to make great cocktails. Actually all we need is a select few quality basic bottles, some bitters, sugar syrup and enthusiasm.
A great guide would be something like The 12 Bottle Bar specifically created to make classic cocktails accessible to the home bartender, with just 12 bottles (or less). It teaches you how to make simple syrup and how to start making great drinks without the expense.
Another place to get some excellent information for the home mixologist would be Jamie Oliver's wonderful Drinkstube - this is a Youtube channel dedicated to showing how easy it is to craft great drinks, with minimum fuss.