Do you have any lip care secrets for maintaining plump lips?

Lips look pretty when they are plump, don't they? That's why you often see celebrities getting injections, only to find their lips look quite unsightly as they age. It seems everyone has a strong desire to maintain full lips. As I get older, wrinkles form on my lips and my cheeks sag, so I can't really smile, and the corners of my mouth seem to droop. The biggest problem is that the volume is decreasing, making my lips look flat. T_T Is there a natural way to achieve lip volume without relying on artificial procedures? Like facial exercises or using lip care products... Please share any tips you have for maintaining plump lips!