First and foremost, use a broad spectrum UVA/UVB - SPF...

First and foremost, use a broad spectrum UVA/UVB - SPF 30 sunblock daily on your face. I also recommend using a good mineral make-up concealer and foundation to enhance, hide discolorations and add protection to the skin.

It is a good idea to use an at-home exfoliation kit. This can be a microdermabrasion, enzyme peel or chemical peel; use only one and no more than twice weekly.

It is also advisable to use products that contain ingredients such as retinol, hydroquinone and other lighteners such as vitamin C and kojic acid to lighten and brighten skin. Finally, in addition to using sunblock, topical antioxidants can be quite helpful.

1.  Daily application of a UVB/UVA sun blocker

2.  Avoid the midday sun

3. Wear a wide brimmed hat

Age spots or sun freckles are a direct result of sun exposure.  Specifically, it is the UVA rays that stimulates melanocytes to make pigment. 

What is misleading about sunscreen labels is that SPF measures only UVB blockage and does not tell you anything about how well it blocks UVA. 

Not all sunscreens that state "UVA/UVB block" are equally effective.  In fact, many have UVA blockers that are not photostable.  In other words, the UVA blocker quickly breaks down with sun exposure. 

There are 2 sunscreens that I routinely recommend for preventing age spots - Neutrogena with Helioplex and Anthelios.  Both block UVA and UVB very well. 

The physical blockers like Titanium and Zinc Oxide also are solid broad sprectrum UV blockers, however, many dislike their thick, whitish appearance. 

Besides sunscreen, wide brim hats, UV protective clothes, etc. are all good ways to prevent age spots.