So, I've read a lot of books now about fashion over forty/fifty, and countless other advice online.
One of my favorites is Kendall Farr's book, The Pocket Stylist.
I'm not a fan of rules, especially where style is concerned, but if there's one I'm learning to swear by, it's this: Learn your body type and what flatters it. I never did this exercise when I was younger. I thought I was a pretty good judge of what works on me, but...at some point it became clear that things have changed. The way I learned what to wear now was by devouring The Pocket Stylist.
I adore this book. Because I was motivated, I followed all her advice. It's taken me a while to get it all, because she answers every question. She tells you exactly what to wear, how long to have your pants, at exactly what point on your middle your shirt bottoms should hit, etc. While it was kind of sad to eliminate some things, it was worth it because....IT WORKS. Now I believe there are no "wrong" bodies, just outfits that are wrong for them.
The second point from Kendall is to buy clothes that fit. Not the size I wish I could fit into, but what fits. Again, this is ultimately freeing because I know the result will look good. She explains exactly what this means. And her advice is so practical and based in good taste that it's really ageless.
I'd avoid online sources about determining body type because there's too much room for error in a short written article. Plus, you never know who writes those things. It could be a freelance writer trained in mortuary science. Seriously. Kendall Farr is a professional stylist for fashion magazines and other media. She knows her stuff. Please read this book.