St. Petersburg - Clearwater International Airport is a wonderful airport located directly across Tampa Bay from Tampa International Airport. It's easy to get into, you can drop everyone off at the terminal entrance and if you have a rental car you're returning, all the companies are located close by. The airport facilities are small, but modern. I assume you're departing on a different airline than you flew in on, since no airline operates out of both airports at this time.
From the Tampa side you'd exit I-275 southbound onto westbound SR 688/Ulmerton Road (Exit #31B) and drive about 3 miles and then take the right exit ramp onto SR 686 westbound. The airport will then come up immediately on your right. From the St. Pete side you'd exit I-275 northbound at Exit #30 onto westbound SR 686. This merges into SR 688/Ulmerton Road, you continue for one mile and then SR 686 continues at the right exit ramp described above. Signage to locate the airport is also good if you'd rather not remember all these state road numbers.
BobK/Orlando