If I have one piece of advice for any fighter, be it an up-and-coming amateur fighter, or a UFC champion, it is wear a suit when promoting your fight. The exception of course is if you are doing a workout in front of cameras. But the rest of the time, if you are promoting your fight, both before and after, wear a suit.
Why? Because of what wearing a suit implies. It says that you are professional. It says that you took the time to dress yourself nice. It shows that you have respect for yourself and in turn for what you do.
If you are trying to convince people to give you money, you want them to know that you care about what you are doing. Would you show up to an interview for that important job wearing torn jeans and a t-shirt? No.
Look at some of the greats through out history in sports. Tom Brady, Peyton Manning, Michael Jordan, Muhammad Ali. All of them wore suits when speaking to the press. Yes their skills in their respective sport earned them respect, but they also commanded it with what they wear.
At UFC 69 after he was defeated, Georges St-Pierre still wore a suit to the post fight press conference. After his hard fought battle with Carlos Condit at UFC at UFC 154, he was seen wearing his suit. All because he knows that appearances matter.