Good tailor, good material. And good construction of the suit itself. The pants should be lined inside so they move with you, not hang and wrinkle. Definitely tailoring, a tailor that knows what they're doing can make anyone, of any form, look like a million bucks.
My personal favorite is a sleek Italian silk/wool blend that isn't ever too warm, and though tapered for form, also conceals a vertical shoulder holster invisibly.
Anything synthetic will look cheap, no matter what.
My favorite formal coat for serious cold in business attire is a vintage black wool opera coat with silk lining, a heavy greatcoat, really, made in 1916 by a tailor in Grand Central Station, NYC. (I found the thing in a thrift store in mint condition.) Every single stitch is perfectly aligned. All done by hand, all done flawlessly. It must have been a very, very expensive rich man's coat back then. I don't think you could find anyone to make anything like that for less than a few thousand at least, today.
That, and don't neglect the shoes. Good Italian shoes vs. outlet shoes can make or break the look of a suit.