The best solution I can think of for this is if you say the vowels A E I O U and really stress the letters as you say them you should notice a difference in 2 weeks.

A good one for the jowls is to make like a fish. Put your head back, look to the ceiling and open and close mouth just like a fish.

I don't think any exercise will prevent saggy skin, but having toned muscle would certainly tend to help support the skin a little better. I would do the facial exercises in conjuncture with a good skincare regimen.

You can buy a book of facial exercises by eva frazer