The brake and clutch fluid are both hygroscopic, so you can check the moisture content with a test kit. My clutch fluid was black when I got my car at 13 year old and 59,000 KMs, I also used a whole bottle of DOT4 fluid, and I now turkey baster flush it anually. My brake fluid was looking darker too, so I did the same, though I should probably do a proper flush. I've read of the clutch pedal not releasing on its own if the fluid gets too dirty.
There is a lot of common sense stuff too, like visually inspecting the hoses, belt, spark plug wires, and other wiring which you should do at least once a year when changing oil, but probably more. I like to give things a quick look over when checking the oil, fluids, and tire pressure, about once a month or before a long drive, and is a good way to keeping up on potential problems or things like rodents building a home. I once had a rat build a pretty nice grass house under the hood of my G35 in about 2 days! If you really want to be thorough, replace the cooling hoses when changing the coolant, and you could probably replace the accessory belt at the same time, though I've always just visually inspected both.
Jack the car up about once a year (maybe when changing the oil) an grab the wheels, suspension, sway bar links, looking for any play or things that are loose. Give the tires a good visual inspection either while jacked up or on the ground, looking for debris, odd wear, and cracking. Tires wear out over time, not just tread life, which is very important with a car that is driven less, so once the tires are about 5 years old by the DOT date code on the sidewall (not when you bought the tires), check them more often, pay attention to their grip potential, and be thinking about replacement.