The older you grow, the more often you need to exfoliate your skin. As we all know, skin cells die and new cells keep getting regenerated. These dead cells come to rest on the top layer of our skin, making our skin look dull, and, in some cases, patchy. Although dead skin is replaced naturally by new cells, this process takes longer as we age, making our skin look duller and patchier for greater lengths of time. This is why regular exfoliation becomes a must.
In your twenties, exfoliate skin twice a week. In your thirties and over, exfoliate skin every alternate day or even daily. Please bear in mind that you need not exfoliate too often if you have sensitive skin as too much exfoliation may cause irritation.
You can exfoliate either in the morning after you've washed your face with a face wash or in the evening. It's up to you really.
I believe that you should do a light daily exfoliation in place of weekly scrub downs. Personally, I exfoliate daily, that way you're always removing a smaller amount of skin cells and your skin always looks fresh.
Look for a light exfoliator that can be used daily instead of the gritty garbage that's out there for five bucks.