Dressing well is never simply about wearing nice clothes. It's not simply about the sheen and surface of appearances unless you wish merely to be a modern philistine. Dressing well is about creating your own story and playing it out authentically, almost as an actor inhabits his role. If you accept this transparency between the interior and the exterior, then you may begin to realize that the cultivated exterior of an individual should point the way to an equally cultivated interior, the character behind the clothes.
Consequently, I will not expound exclusively on topics of apparel (i.e. the virtues of "bespoke" tailoring, the history of Savile Row tailors or the virtues of Neapolitan sartorial style). I am neither an expert on these matters nor is that the heart of the matter. What I propose is quite opposite. In order to dress well, one should start not with the material elements of dress but with a careful examination of yourself and the situation you find yourself in.
The well-dressed man, like the skillful author, does not reveal everything about himself (or his characters) at once. Rather he offers meaningful insights into his world to those who are able to reciprocate.
In order to create your own story, you need to understand the key elements of any sartorial narrative. Here they are:
Daytime business, semi-formal & formal
Cast of players
Suits and jackets
Shirt and tie
I have offered here the raw elements of your narrative but it is up to you to provide the necessary spirit and substance of your story.