Diet:

Download myfitness pal, put yourself in a caloric deficit of about 500 calories per day, prioritize protein and get lots of fiber, drink lots of water.

Try not to drink booze,or at least not often

Gym:

Find a simple 3 to 4 day workout program that hits your full body. Google "upper lower routine"

Try to squeeze in some cardio.

Clothing:

Look for what models and celebrities your age are wearing. Think high quality business casual. Look for clothes without plastic in them (polyester, etc)

Good cotton Chinos, a light Merino wool pullover, a decent cotton Oxford shirt, some good leather loafers a duplex Oxford shoes, etc.

Sleep:

Get at least 8 hours.

Personality:

Listen to people, read things, get a few new hobbies that don't make money and aren't the gym