Clean the driveway throughly. You want to get up any foreign substances and removal all the debris.
Power washer the driveway. Use a rotating tip on the power washer, it gives the same strength as a single tip, but you can cover much more surface at once. Work in slow circular motions. This step can take several hours to all day depending on the size of your driveway.
Although you don't necessarily need to, I'd highly recommend acid washing the surface. The gives you a good fresh slate to work with. Check out the resources section for instructions on how to acid wash if you haven't done that before.
Once the driveway is clean, it needs to be dry before moving onto the next step. This can take days or just hours depending on your weather. A leaf-blower can speed the process along. Check for dryness either with a moisture meter, or by sticking a piece of masking tape down. If the tape sticks, the driveway is dry. Make sure to test in several spots to insure the whole driveway is dry.
Now you are ready to reseal your driveway. Put the sealer in a five-gallon bucket. Some driveway sealers need to be mixed with xylene, and some need multiple coats, make sure to check the sealer you have. Attach the roller stick to the frame and put the cover on.
Dip the whole roller frame in the sealer and start rolling it out on the driveway. You may want use a brush around the edges. Do one pad at at time, and then back roll the entire pad by going the opposite direction with the roller without adding any more sealer. This is just to make sure you have the sealer down evenly.
Wait! Don't touch it when it gets blotchy. This is just how it dries. Once the whole driveway is dry it will be the same color. If you try to touch up before the drying is compleate, it will end up uneven.
Keep cars and people off your driveway for a few days until it is ready to be back in use.