I'm 40-how can I quickly improve my complexion?

Use mineral makeup. It’s a lifesaver for skin!

Cleanse, moisturize and like @KatetheGreat said, mineral makeup is awesome. Not only is it better for your skin, it looks great!

Drink a TON of water (the 8 glasses a day thing). It helps more than about anything.

Avoid greasy foods and to some extent dairy products (in particular milk).

Don’t wear make up when you don’t have to, it clogs your pores, even the kind that are supposedly good for your skin. No make-up always beats make up for clearing complexion.

Vitamins help believe it or not.

Avoid having things maintain contact with your face, like a football helmet or your hand if you’re bored and slumped on a desk or something. This again blocks pores, and traps sweat to your face.

Some kind of night time and morning face wash will help. In a pinch if you feel a zit or something coming on, you can apply most tooth pastes to it overnight, and it will fight it (weird I know, but totally works).

Do as I say and not as I do.
Drink lots of water as stated already by those who know.
Wash your face morning and night.
Use a moisturizer for your skin combination.
Sunscreen!
Water water water… I see the most difference when I am hydrated.
proactive is great for occasional breakouts too, even at 40.

No zigs here…just looking for smooth.

Absolutely agree with @tedd and @gravity. Having beautiful skin has more to do with what you put into your body than what you put on it. Water… and lots of it. Eat a healthy diet with lots of vegies and fruit. Avoid harsh chemicals. A gentle exfoliant would help if your skin isn’t smooth but make sure it isn’t too harsh. Avoid being out in the sun too much. A little is fine, but do wear sunscreen.

Eat healthy food and drink. Get fresh air and exercise. Bathe and wash your face, though not too frequently.

Water only helps until your hydrated, after that you just pee it out. They have done studies, even Dr. Oz did a nonscientific one on his show with twin women, and the woman who drank more water had the same hydration in her skin as the one who drank less.

Eating healthy does help. There is actually a diet for healthier looking skin, can’t remember the name of the book.

Get a really nice exfoliator, Clarins for faces is extra gentle, really good. Only exfoliate once or twice a week. If you can use chemical exfoliators like AHA, that will help erase little fine lines, but they can be irritating. If you can afford it I think Chanel face lotions are the best. I know “they” say the cheap ones are as good as the expensive, but Chanel feel great.

Use SPF every day to protect your face from further damage, and some sun damage can reverse.

Drink lots of plain water
Wear sunscreen and nightcream
Don’t sleep on your belly
Clean your face (makeup) with warm water on a cloth with lotion instead of soap.
Buy a good exfoliant cream for a few night every month.
Wear colored lip glosses rather than matte or pearlized lipsticks
Use concealer (lightly) under eyes, around nostrils or anywhere there are broken capilaries.
Use a blush on your cheeks.
Have a salon style your eyebrows to fit your current face rather than the one you had at 15.

I don’t agree with washing your face twice a day at 40, maybe a hot water rinse at bedtime and good moisturizer. A lot of tests were done that showed nurses were washing the skin off people with the twice a day.

There’s a 40 year old woman I know who is the most beautiful woman I have ever seen in real life. She has 4 kids. She is literally more beautiful than any other woman I know, at any age, including women in their late teens and early twenties. She drinks two liters of water by noon every day and swears by it.