I started treating my body as soon as I started learning about makeup, months before HRT was even considered. I was curious...but one of the first things the books said was, "Take care of your skin! When you're older, you will thank yourself!"
Protect against sun damage...don't be eager to get a "good" tan (i.e., a dark one). Whatever your natural skin tone is, that is natural, and good. Yes, if you're outdoors you will get a tan...but less is better. If you've ever seen a farmer or other outdoor worker, you will notice they age much faster than indoor workers do.
Sunscreen (30 spf is best, more than that isn't known to do much more protection) all exposed skin, wear light colored clothing, use skin lotion (I use the cheap stuff, but YMMV), don't expose your hands to harsh chemicals (oils, strong soaps, "Comet", etc) Your hands take a beating, and if you don't want "man hands" treat them like they're lady's hands ASAP. Even if you've been harsh to them for 30 years...start now, and the damage will stop where it is now. With luck, they'll heal some, too.
Pamper your feet, as well.
That's the outside...now pamper the inside too. Cut back on alcohol, don't think "I can have 3 drinks now, I'm a lady!", think "One or two drinks is enough for my 'needs', I love my liver!" Eat healthy. Remember that what is good today, will be declared evil tomorrow (Bran comes to mind, as well as every diet out there).
Be balanced in your food, in your life, in your private moments. Control your finances. (Yes, this isn't specifically a woman's issue, but if you haven't learned it as a man, you MUST learn it as a woman!) Don't buy things unless you truly need them. I don't even read the catalogs I get in the mail, I just chuck 'em. I know their marketing will persuade me to buy something...and I don't need that.
And finally...Be happy. Don't let contentious people into your life.