Break it in.
After all the decisions, all the fittings, the hours of handwork that have gone into your suit, you are ready to stride into the world. That's not to say you should show off the newness of your suit: Fred Astaire supposedly threw his against the wall so it appeared worn in. You don't have to go that far, but the suit should look as though it's been lived in. You should be wearing it, not the other way around.
You'll still need to take care of it. Keep it on a wooden hanger so that it keeps its shape, and don't wear it two days in a row, which allows wrinkles to set. Also – and this is important – don't dry-clean it. Sponge and press it when you have to. Many tailors offer this service themselves, or they can refer you to a trusted location.