Evaluate the Web site that you're sending
traffic to, and gauge whether the keywords you'll be targeting have changed. Did the client launch a new product? Perhaps keywords that weren't strong traffic drivers last year may be more relevant
now.
Gauge whether your ads are directing users to the right landing pages--and whether the landing pages are still functional. Perform a sweep for nonexistent or broken links. And make sure that the ad copy itself is still relevant, as there's nothing worse than reeling a user in with an offer that your client can no longer fulfill.