Preventative maintenance is important in that you repair a problem before it becomes a problem. Why wait until you are on the side of the road in rainy weather at 10:00 at night to replace, say, a bad radiator hose. Do it on a nice Saturday afternoon in your garage or driveway. It'll be more comfortable and you will have one less thing to worry about as your out driving.
1) DIY: Replacing Your Fuel Filter
Fuel filters are often neglected until they start to clog up. When they do, your vehicle will lose power and hesitate. Even the fastest sports car will have the get up and go of a 1969 VW Beetle with a clogged fuel filter.
2) DIY: How To Replace Your Heater Hoses
One one the most common sources of coolant loss are the heater hoses. Over time these hoses will get hard and brittle and can crack or break at the worst possible times. They are easy to replace and a lot cheaper to do so at a time and place of your choosing.
3) DIY: How To Replace Your Windshield Wipers
In order to drive safely in even the worst weather you need to have good windshield wipers. Unfortunately wiper blades are like a leaking roof, you only think about them when it rains. I recommend replacing wiper blades every year, preferably just before winter hits.
4) DIY: Replace Your Timing Belt
The purpose of a timing belt is to provide a quiet, flexible connection between the camshaft and crankshaft to keep the valves opening and closing in phase with the movement of the pistons. If they break at a time of their own cgoosing, severe engine damage could result. It is much cheaper and easier to replace it at the recommended intervals.
5) DIY: How to Change Your Spark Plugs
Spark plugs are one of the most important parts of your vehicle. They are what ignites the air/fuel mixture that gives you the power you need when you need it. As they get old they wear out and can start to misfire, causing power loss or engine stalling. On most vehicles they are easy to replace and should be every 30,000 miles or when recommended by the factory.
6) DIY: Repairing Paint Chips
Now maybe this doesn't sound important, but it could save you hundreds, maybe even thousands of dollars in repairs. A paint chip exposes the bare metal under the paint. Once this happens water, road salt and acids can start rotting out the metal and left unrepaired, leave big holes in the sheet metal.
7) DIY: Winterizing Your Car
This is an important PM job in that it assures you your vehicle is ready for the coldest winter. I recommend replacing the coolant every two years and checking the heater and radiator hoses at the same time.