Although I'm not one to do a lot of planning, I'd suggest you come up with a rough itinerary before your visit. Split the Park into three sections - East (Rio Grande Village and Boquillas), Central (The Basin) and west (Castolon and Santa Elena) and outline the activities you'd like to do in each. The Park's
website has some great suggestions depending on the amount of time you have. It also has fairly detailed information about hikes and drives. You'll get a Park map when you enter but consider picking up a more detailed one by National Geographic which is available on line or at various stores such as REI for around $12.
Some of our favorite drives: Old Ore Road (short hike to Ernst Tinaja), River Road East to Mariscal Mine, Glenn Springs to Pine Canyon (and the hike to the pouroff), Old Maverick Road. Check with the staff for road conditions when you arrive.
Favorite hikes: The Window, Lost Mine Trail, Emory Peak (and up to the South Rim if you really want a workout - we usually overnight on this one), The Chimneys, Boquillas Canyon, Santa Elena Canyon, Mule Ears Spring, Tuff Canyon and of course the Hot Springs.
Food: The restaurant at the Lodge is usually good. The Starlight Theater in Terlingua is very good and a great atmosphere. La Kiva is a unique local watering hole in Terlingua with a bit of mystery (we haven't eaten there since Glenn's death
A murder in Terlingua, TX and
Badlands, TX.
Other: Be sure to visit Terlingua even if you don't eat there; pull up a chair on the front porch of the store and ask a local about the Burro Lady. Visit her grave in the nearby cemetery. The drive from Terlingua to Presidio is nice and you may want to stop at Big Bend Ranch State Park if you have time.
Have fun and post back with details of your trip.