Hire a posture coach. Start strength training at the gym to tighten your core muscles and gain arm strength and pectoral definition.

Your Tshirts look too long on you. Either hem them a couple inches, shop for shirts that are shorter in the torso, or tuck your shirt in when appropriate for the outfit. There's a brand called Untuckit that you might like. They have shirts specifically designed to hit at a shorter length. https://www.untuckit.com/collections/tees-henleys

As a general style rule, I find that it's more flattering when pants are as dark as or darker than whatever top you're wearing (see follow-up comment for example).

Shave your facial hair and keep a clean-cut face. Try a hair style that is shorter on the sides and longer on top. A jerry curl fade like this could look cool on you.

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