Keeping up with your tools maintenance isn't very hard or time-consuming. One item you want to pay particular attention to is your power tool motors. Most manufacturers are using brushless motors, so this doesn't apply to those types of motors. This is for your tradition motor that uses a copper wiring with brushes.
After you are done for the day, take a couple of minutes and blow some air through the vents to get loose debris away from your motor and contact brushes. By taking a couple minutes and doing this, you can add years of life to your tools. This keeps the motor running cooler. When your motor runs cooler, the brushes will last longer. They last longer because the motor will not heat up. Heat kills motors.
Even if your motor is a brushless motor, take the time to clean out your tools when you are done for the day. As you know, power tool are expensive. If you can get a couple more years out of them because you take care of your tools, why not take the extra time.
For brushed motors, most small motors have two brushes, a solid block of carbon graphite. These conduct electricity to the motor and make the tool run. Well, after time these wear down due to friction and will gradually cause the power tool to lose power. The loss of power is one clue to replace the brushes, but another way is if you see sparks inside the tool housing. The key thing to look for is the amount of sparks. If you see a couple sparks here and there, that is common. When you start seeing a bunch of sparks, then you know the time has come to replace the brushes. The good news is brushes are usually very easy to replace.
Somewhere on the power tool, you should see how to remove the housing. If you can not figure this out, take a look at the schematics in the owner's manual. Once you get the housing off, you will be able to see the old brushes. They can be removed very easily. Once you have everything off, brush off the dirt inside the motor. Try not to use compressed air as this might cause the small particle to get into the motor and other switches. Some power tool will not require you to move the whole housing. Some power tool have small screws that can be removed and the user can have easy access to replace the brushes.
Before you start any project, always look up the prices of a new tool and brushes to make sure it is worth replacing the brush. Sometimes it makes more sense just to buy a new tool.