1. Your Body Is 60-70% of Looking Good
Be lean, have visible muscle, v-taper, thick neck, etc. There's only so much clothes can do to cover up an unattractive body. A lot of attraction comes down to health cues (e.g., clear skin, not overweight).
Don't believe dorks that think most people can ever have "too much muscle." That will only happen if you're on steroids, a 10+ year powerlifter, or the gym completely absorbs your life. If you lift and do cardio 3-4x weekly you will look good regardless of context.
2. Outsized Returns Come from Going Slightly Upmarket
Rather than Zara or H&M, spend 20-30% more and go to Massimo Dutti, Reiss and so on. You'd be very surprised how much more you get for your money. More expensive brands and you quickly get diminishing returns.
3. Fit, Quality and Cleanliness Are Orders of Magnitude More Important
After your body, fit, quality and cleanliness are orders of magnitude more important than any other metric.
4. Avoid Micro-Trends and Flashy Brands/Logos
Goes without saying. Brands and logos are cheugy. Don't confuse trendy/expensive with looking good. I would even avoid "statement pieces" as they don't work with the rest of your wardrobe. Don't confuse avoiding trends with never adopting new silhouettes. Obviously a suit from 40 years ago will look bad now.
Fashion Trend Levels
Fundamentals: Quality is king, this is always a truth
Meta-trends: 8-10 year cycle, specific fit (e.g. 2003 NBA draft suits look like shit now)
Trends: Whatever the industry is pushing in that 3-5 year period (e.g. crocs are in)
Micro-trends: Esoteric social media stuff, should usually be ignored (e.g. fashion guy wearing baggy, square jeans and Arc'teryx)
It's up to you to decide what to follow.
5. Fashion Is Fundamentally About Social Signalling
Class, in-group/culture. It's an effective social tool. Dress according to what/who you're trying to portray to the world. "Would the person I want to be wear this?"
Anecdote: I noticed on the first day of university, everyone who dresses the same immediately forms groups. Everyone has a personal brand. What is yours? Be consistent.
Reference: The Appearance of Power: You need to decide what your archetype and sub-archetype is.
6. No, You Don't Need to Be "Comfortable" All the Time
Stop wearing sweatpants everywhere. The reason people say "don't judge a book by its cover" is because absolutely everybody does, all the time. There's nothing you can do about this other than be aware of it and use it to your advantage.
I understand trying is corny nowadays and it's cool to be nonchalant, but I encourage you to be chalant. How about you actually lean into putting effort in? Err on the side of over-dressing.
7. Accessories Are Highly Useful
Watch, bracelet, belt, tuck your shirt in if applicable and so on. Don't overdo it or you'll come off as "try hard."
8. Don't Miss the Basics
Shower, shave, nails, skin, hair, ironing, don't overdo aftershave.
If you're socially retarded no one will care you're dressed well. Be a well-rounded person.
As with most things nowadays, 60-80% of people don't try, 15-35% try but half-ass it, the rest actually pull it off. So long as you're doing things intentionally you'll be far ahead of others.
Also, don't forget context switching. You will have to dress differently for the office, gym and hanging out with friends.
