A tailor will ask you straightaway when you are going to wear your suit. Have an answer ready. Do you wear a suit to work? Do you dress in jeans, and is this going to be your only suit? Are you going to wear it to your wedding? To your sentencing? A tailor wants to build a relationship with you, so help him understand your needs. And don't be afraid to speak freely: Tell him what you do for a living, what your office is like, where you live, what the climate is, what problems you've had with suits in the past. If you generally don't like wearing suits, tell him why.
Don't feel pressure to act more formal than you are. If it's the first time you've been to a tailor, tell him that, too. He won't think you're a greenhorn; he'll be flattered you came to him. Remember: He's been dealing with men for many years. He's seen all types.
If you want to wear a suit to a special occasion (say, your wedding) then work it into the rotation, you can ask the tailor to put on special buttons for the big day. Then you can rotate them out for the rest of the life of the suit. Keep the buttons, of course, and pass them down to your son.