There are plenty of "rules" attached to how to dress, especially in the realm of menswear and, more specifically, tailoring. While some could be deemed old-fashioned, there are certain points that still warrant attention – and for good reason. Do not worry, there is still plenty of room for self-expression. In fact, your whimsical affectations will have more gravitas when they are grounded with the below guidelines.
1) Only one buttonhole in the lapel
The lapel buttonhole you see on jackets today evolved from military tunics, which were originally designed so the lapels could be folded up and fastened, attaching to a button underneath the opposite lapel. This detail was adapted into everyday wear, as it was a useful position to wear a flower, and thoughtful tailors even added a loop to the underside to keep the stem in position. It's also an elegant place to keep a watch-chain attached to a half-hunter or, perhaps, a cigar cutter. But there is no reason on God’s Earth to have two parallel buttonholes in one lapel. They are a favourite with local newsreaders who may even select contrasting tones just to be “different”.
2) No belt-loops on formal wear
Belts have their place. I prefer suits where the trousers are self-supported or suspended by braces but many well-dressed men wear smart leather belts with their tailoring. However, they have no place in formalwear. Trousers worn with morning dress should have side-adjusters and/or buttons for braces. The glimpse of a belt under a waistcoat is unsightly at the best of times. Wearing a belt with black tie is a privilege reserved for waiting staff. For white tie (evening tails) I actually do not even like side-adjusters and prefer the trousers to be exclusively for braces.