When you arrive in front of the tailor/salesman, he will certainly ask your opinion on many details you never thought of. The width of the lapels, the number of buttons, the number of slits on a jacket... In short, you will certainly be lost, so here is my list of details that make a good men's suit and that you should follow if you don't have any experience in this field. You won't be able to go wrong anymore!

I'm talking about the important points to choose a classic jacket, for a beautiful wedding suit or a suit that you can wear in all occasions. Once you have your basic suits, you will be able to venture into cross-over models, with patch pockets, etc!

Reverse notched: around 9cm wide, but avoid taking less width, especially if you have a good corpulence.
A buttonhole on the left lapel: this will allow you to hang a "lapel pin" or a flower on occasion. Ideally this buttonhole will be a hand sewn "Milanese".

Two-button closure: this is the classic buttonhole on the front. We button only the top one and never the bottom one.
Four buttons on the sleeves: no more and no less. It is the perfect balance. You can have functional buttonholes, it's a charming detail.
Natural horn buttons: choose a beautiful dark horn.
Two piped pockets with flap: this type of pocket is to be preferred if you should have only one suit. Patch pockets are more casual. A small "ticket" pocket above the right pocket can be a nice detail.

Two slits: on the back of the jacket. Not one. Not three. Two! Make sure that they are well closed when you are standing at rest. If they are not, ask your tailor to pull up the opening of these slits if you have a fairly pronounced buttock.
A chest pocket on the left: I don't see how we could put it somewhere else!
Flexible shoulder: a jacket with little structure - "unstructured shoulder" - gives a suit that is pleasant to wear and that fits the shape of your body without making you look like an American soccer player.

For the pants, privilege sobriety, comfort and high sizes, it is the best way to enjoy them to the maximum. Buy a second pair of pants with your suits because they wear out much faster than jackets.