It's Business, It's Casual.
Dressing well is an art whose skill anyone can master with practice, observation, and knowledge.
It isn't always necessary to wear a suit in order to be svelte, and if that was a doubt, take a second look at these photos. The trick is simple: one must learn the basics and then alter them to fit their body, image, and style. Mistakes will be made from which lessons will be learned, that is if you are observant.
The key is to dress down to dress up. Stripping away the suit jacket and the slacks, a simple vest paired with a dress shirt and a tie will retain that elegance. A pair of jeans in lieu of slacks or chinos projects a more relaxed aesthetic. The rest is quite easy as it can remain the same - spruce it up with accentuating touches and select a pair of any style of shoes.
One can be well dressed and still have some fun. After all, it's business, it's casual.