All good comments above but I will add one. Make sure the "ground temperature" is above 60 degrees, meaning the actual ground temp. You will notice that most reputable places only sell driveway sealer in the late spring, summer and very early fall timeframe. Just because it is 70 degrees out on an April or September day does not mean the ground is warm enough to apply the sealer. Watching it wash away a week later in a heavy rain really.........well you get it.
This is the product that I used. Great stuff, easy stir and easy cleanup.
http://www.latexite.com/pr-optimumPRO.html
BT