First things first: Park the car and jack up the front. Remember to set the parking break. And if you've been driving for a while (say, to the auto parts store), remember that engine components may be hot enough to burn you.
Now, using your tire iron or spinner, take off one of the front wheels. Take off the brake caliper. You'll probably need to remove bolts to do this. Remember to keep bolts in clearly designated areas, so you know which bolts go with which parts. Slide the caliper off the rotor.
The brake pads are on the inside of the caliper. Depending on the car, you'll see bolts, springs or clips attaching the pads to the caliper. Undo those fasteners.
You'll notice that the new brake pads are thicker than the old ones. That means you'll have to adjust the piston to accommodate the new thickness. Open the piston. When it's fully open, it will be closer to the center of the car than to the wheel. You might be able to open it with your bare hands, but if it puts up a fight, use your vise grip or channel lock to push it back. You can also use a C clamp to get it open. Get the lips of the clamp inside the piston, and then open the clamp. If you go this route, though, make sure to protect the surface of the piston somehow. And be aware that a too-tight piston may signal caliper problems [source: Memmer].
Opening the piston forces fluid back up into the hydraulic system. Professional mechanics take the precaution of lowering fluid in the piston's reservoir before raising the car on the jacks. If you skip this step, just be aware that the reservoir might overflow.
Now it's time to replace the rotor, if you're doing that.
Before you put on the new brake pads, break out the brake pad grease. Put it on the side of the new brake pads that will face away from the rotor.
You're more than halfway done. To find out how to put on the new pads and road-test the car, read on.