When you want to seal coat asphalt, there are a number of steps to take to do it properly. The first step is to trim back the grass that's growing near the asphalt. You don't want the grass to get in between the seal coat and the asphalt.
Then, use a powerful blower to get rid of the dirt and debris that is on the asphalt. The entire length of it should be clear of anything on top of the asphalt.
Next, it's a good idea to use a power washer on the driveway to get rid of even more debris. Then, use a high-quality crack filler to fill in any cracks in the asphalt so that it's far more smooth. When this is done and everything is dry, you can start using the seal coat on the surface of the driveway. This is applied with a sturdy brush that can spread it with a back-and-forth motion.
Start on the edges and fill those in first. Once that's been done, pour a couple of gallons of sealer onto the driveway and move it around with the brush. Spread it throughout the driveway, all the way to the edges to make sure everything is sealed.