For questions like this, I refer to the Good Book, which says ashes to ashes, dust to dust. What it doesn't say, is this process starts along time before we pass.
As people get older they tend to get worried about their appearance. A few wrinkles or crows feet and they go into a panic mode. Young looking skin is considered to be beautiful. An effective anti aging serum is a more effective way of doing away with signs of aging.
I use La Mer. I find it is good, however the performance does not fully justify the price paid. It is an expensive product, and the main moisturizer of La Mer (their flagship creme) does such a good job that I find myself omitting the serum step most of times.
Drinking plenty of water, sleeping really well every day (at the times of day that make YOU happy and truly relaxed) and living a low-stress life are measures against face aging that no serum in this world can ever achieve.
If for whatever reason one wants to use serum, La Mer is indeed one of a few very good options out there in the market. However it must be worn daily, preferably am and before bed. In combination with drinking plenty of water, sleeping well, etc. one should expect to see a +15-25% difference on the skin in a couple of months time.
I've found that using liquid vitamin E is good for any part of your skin. You can get a bottle of the liquid stuff at any health food store. Or you can get vitamin E caps. instead of the liquid. Just pierce the cap. and squeeze the oil out. It'll be quite greasy so be careful of clothing, furniture, whatever. Leave it on for an hour or so and wipe it off. You can use it whenever you want, its very good for the skin.
I have tried Nivea (active firming), L'Oreal (vita lift), Boots (anti age serum), and L'Occitane (Cade Youth Concentrate). L'Occitane Cade Youth Concentrate appears the most effective.
Using sun screen and keeping the skin hydrated - take a look at people that live in dry warm climates or for that matter dry cold climates. There is no question that baking in the sun is the worst thing you can do for your skin.
You can add smoking to that.
I really like L'Occitane Youth Concentrate. It moisturizes well and contains imortelle extract, which helps you look younger supposedly. I do notice that it takes away any blemishes or any marks that you may have on your face and makes them lighter. It also smells like a cedar closet, which relaxes me.
You can put Vitamin E oil on at night which is sort of like a serum, though it is messy and I rarely do it, but it's very reasonable in cost. I got mine in the grocery store, comes in a little clear bottle with a push pump.
For something less messy you can try Reviva Labs Alpha Lipoic Acid, Vitamin C Ester & DMAE cream. This is also for night. You can find Reviva at health food stores like Vitamin Shoppe. But this is a cream not a serum. Works well.