Wash

Driveways should be cleaned on a somewhat regular basis (at least 2 times a year). If you have a power washer, use that, otherwise a hose with a strong stream will do it.

With a power washer, you can use driveway cleaning solutions to add a little soap into the mix. If you don't have a power washer, use a bucket and a stiff brush.

Obviously, not all driveways are created equally so this could be quite the project depending on how long and wide it is. Concrete is like any other porous material exposed to the elements; your looking to wash away salt, acid from rain, from car exhaust, from general traffic, etc...

Repair

Secondly, you'll want to repair any cracks in the concrete. Cracks in expansion joints can be filled in with a non-hardening UV safe silicon, while cracks in the actual driveway should be repaired with a concrete repair mortar.

In colder climates, water can get into cracks and when it freezes over winter, it can cause the concrete to shift, causing more damage.

Seal

If you choose to, you can use a concrete sealer; this is usually rolled on and seals the pours in the concrete to prevent water penetration and generally makes it easier to wash the concrete the next time around. You'll do this about once a year.

You can go a bit extreme and use a concrete epoxy with some aggregate (sand) mixed into it to further protect the concrete. This is usually used in a garage to provide an easy to maintain and clean work surface, but this can get expensive and is usually found in automotive shops.