I've learned many things, including:
Don't be in a rush to build a wardrobe. It's a journey, not a race.
It's better to have 2-3 perfectly fitting suits than 10 that you're not completely satisfied with.
Learn to shine your shoes nicely. There is no need to own 20+ pairs of shoes (I have failed at this and spend too much extra money money).
The fit of a shirt is much more important than the name on the tag.
Things like pant rise, front style, length, and taper, are extremely important. Know what works for you.
If you spend a lot of time in casual wear, spend time and money on your casual wardrobe. I wear my Samurai jeans way more than my suits.
Use sneakers for sports, wear proper footwear like shoes or boots at other times.
Ties, watches, belts, and shoes can make or break your look. Choose wisely.
Try stuff on. If it does not fit perfectly or it can't be made perfect, don't buy it. Something else will come along that is better.
Get yourself in as good of physical shape as possible and try to maintain it. No piece of clothing can make up for you being overweight, having poor hygiene, etc.