If you want to look like a boss in your waistcoat, remember these points:
You should choose the right waistcoat length for your trousers. The waistcoat must cover the waistband. Hence, based on your height, the rise of your trousers, and your torso length, your waistcoat should be distinct.
Authentic waistcoats should always have a lined back. The back must be smooth so the jacket will drape and hang properly.
Your waistcoat should have big armholes so it won’t prevent the motions of your arms.
If you wear a waistcoat, avoid the belt in favor of braces or side adjusters. After all, belts will always make the waistcoat different from the trousers’ waistband. And this looks crowded and bulky.