Regular fluid changes are the most important thing you can do. Change oil every 5k miles or once a year at least, antifreeze every 3-5 years. I wouldn't touch the transmission fluid at that mileage unless you know it was regularly serviced, which isn't likely. Baby the car and don't beat on it. 

Regularly check under the hood and under the car for any abnormal drips or leaking, oil change time is good for this. I routinely do it with a 266k mi 1999 Ford Ranger, and I think of them as pre-flight inspections. Sometimes I find something that needs monitored. I blew a coolant hose a couple weeks ago and noticed the antifreeze puddle in the parking lot right away. Be willing to do preventative maintenance on things before they become a bigger issue. 

Fluid changes and following the factory recommended service intervals are about all you can do.