It seems like for serious sagging plastic surgery of some sort is in the cards, or maybe some of the newer thermal "tightening" procedures that come with their own risks, as there really aren't any "firming creams" as such(contrary to what the skin care manufacturers would like to have one believe). Maybe a good set of facial exercises like what SusieQ referred to might help ward off worse sagging? I have no experience with facial exercises though.
Aside from that, I'd go along with what makinalist said, according to your skin's tolerance. Some of the real anti-agers(Rx retinoids and skin lighteners, medical chemical peels)can be quite harsh for some skins - there's a reason why they're Rx. If you're not on a good sunblock, get onto one now - it might not undo damage but it might help keep things from getting worse.
If you're still not sure as to what products, a visit to a good dermatologist could set you on the right track and you wouldn't be wasting your money on stuff that has a lot of hype but really doesn't work. But chances are they will recommend a good cleanser and moisturizer according to skin type(doesn't have to be expensive), sunblock worn year-round no matter what the weather, exfoliation as tolerated(anything from a glycolic cleanser up to stronger leave-on products)and a retinoid, and an eye cream if you want. The retinoid can be an OTC retinol product(especially good for a beginner or for someone with more reactive skin)all the way up to Rx. If you get those few things in place that's basically all you need in the way of home skin care. Said dermatologists often recommend some perfectly good drugstore products, in addition to a targeted Rx product or procedure.
On the general health front, which does affect the state of one's skin as well, be sure to get enough fresh foods in your diet, plenty of water and exercise, get enough sleep. Last but certainly not least, really watch the sun exposure. A lot of collagen and elastin(what keeps skin nice and firm when younger)damage happens from a lot of unprotected sun exposure. A little is good, but a lot is NOT better. Best of luck with this!:)