Although it might sound obvious to many of you experienced gentlemen out there, but did you know that tradition dictates that you should always leave the bottom button on your suit jacket undone?
So, if you have a 3 button, only fasten 2 and with a 2 button you should only fasten 1.
For what concerns sleeve buttons, they are fake/not working on commercial suits, while with high-end and custom suits, you will see opened sleeve buttons (aka working cuffs). Some call it a “show-off” some call it a “personal style detail”. I will leave that up to you.