It's been 7 years for me as well. I'll echo everything April said already. And add...
Proportion is a huge one, especially for those of us who are petite. I've learned that I can wear virtually any style, as long as the proportion and fit is right. I can create the illusion of a pear shape or hourglass shape etc as the whim may strike. And that while I may be petite, I actually do not have short legs -- my legs are proportionately average. This is huge for me as I got teased growing up for my supposedly "stubby" legs, and I grew up with a mom who's a pear and a sister who's an hourglass, and so I believed that was what a woman was supposed to look like, rather than an IT apple with scrawny hips and barely defined waist. Actually, YLF helped me find my waist -- it's just up higher -- and showed me how to accentuate it, then later on, to surrender it because why not.
Capsule dressing was a godsend, especially when I took on this new job with all the travel. I no longer check bags or haul around a bag that's weighted down with too many shoes and clothes that go unworn.
Learning the power of "third piece" -- a topper or accessory - to elevate a simple outfit. Huge! I never wore scarves or belts before YLF. I've never had more fun with handbags either! And these things always fit and are easy to find. And now my wardrobe just will not function without the critical jean jacket, leather jacket, blazer, or cardigan.
Incorporating color, texture, shine, pattern into an outfit. If I want to wear all black, it will work if I add some texture and shine... and a pop of white somewhere livens it up.
Learning why I don't like some clothing items like jeans or starchy button downs. It's not just because I find them uncomfortable, it's because my body type is more soft than angular. So I roll with it and choose softer more flowing clothing that moves and stretches, like a silk blouse instead of a button down. Or I wear ponte knit pants and then add denim on top to casual it up.
Disguising my midsection! Patterned tops that flow out away from my belly, then either half tuck or cinch in with a cardigan buttoned just once to create an X.
It's not only okay, it's preferable, to keep the makeup routine simple and minimal. I stopped trying to wear eye shadow and eye liner (always looked goofy on me as my eyes are hooded) or blush (don't need it as my face is naturally red) and have never looked back. Moisturizer, light foundation, mascara, and lipstick is all I need.
Embracing the colors that flatter my skin tone (murky tones), rather than wishing I could wear yellow and orange.
The best lesson of all? Seeing real women wearing real clothes. I'd rather spend my time browsing the WiW's here, than reading a fashion magazine.