Most important thing is to start wearing simple clothes that fit well.
Get rid of all your graphic tees and any hoodies that aren't plain colors or subtle patterns.
Obviously you can keep a few with sentimental value to wear at shows or around the house.
First thing is to get your measurements taken and figure out what size stuff you should be wearing because I'm gonna guess everything you own now is at least one size too big for you. Clothes should be fitted and trim but not skin tight.
Next figure out what colors work with your skin tone. Google can help you with that. When in doubt, start with a palette of earth tones like olive, browns, burgundy, navy, etc.
Go to a basic store like uniqlo or even H&M or Zara. People are gonna rip on you for supporting these big fast fashion companies but if you're restarting your wardrobe from scratch that's a good place to start.
Get like six plain crewneck shirts in a few different colors. Maybe get a few white v-necks if you like wearing undershirts under collared shirts.
Pick a few plain or subtly patterned collared shirts for work. I'm not sure what sort of office you work at but it sounds like if you can get away with your current wardrobe the dress code isn't strict so you don't need many formal shirts.
Buy a couple pairs of darker blue jeans without a weird wash and maybe a pair of black jeans. Jeans should be regular or slim fit and should end at the tops of your shoe laces.
Get some chinos in khaki or grey or olive for more dressy casual situations.
Get a plain sweater that feels nice or has an interesting texture.
This is just basic advice to start. As you start caring more you can start learning more.
From what you've said it sounds like you'd get good advice from the folks over at the /r/malefashionadvice on reddit
People here hate on Reddit so much but there's really no better place to learn to dress well by most peoples' standards. This board is mostly young '90's fetishists at this point.
