First Zihua Trip!

Avoid the time share sharks offering you a free ride and go right to the taxi counter and buy your "ticket" for the taxi there. If you don't have Pesos on arrival, head to your left out of customs/immigration and get them at one of the ATM machines. Use Pesos to pay for everything, especially with the current exchange rate.
Walk along the beach to Las Gatas for a nice beach day. We like Otillia's and Franco's antics. Although it has never happened to us, others have commented that his math on checks is sometimes "fuzzy." We've heard good things about all of the restaurants there.
Go to Barra de Potosi one day. You can taxi ther, but it would be mor fun to bus downtown then bus to Los Achotes and the take a Pasero from there to the beach. You'll save quite a bit and its a lot more fun to go that way.
The archeological site to the south of Los Achotes is well worth a trip, you really need a guide for this. The guide that took us there is sadly no longer able to provide the service. I'm sure others here can give you some tips.