back in high school (80's) i had a job for about 4 years as a mobile pressure washer.
we did everything from pools to houses/driveways to trucks etc etc etc.
concrete driveways were always the easiest, if you have heavy oil spots/stains then you'll want to "pretreat" them with something that breaks down the oil....we used to use dawn and scrub but i'm sure there is something better nowadays.
the pressure washer with a 5-10 degree tip should make it look brand new, be carefull around the edges and in the cracks...you don't want to remove the "grout" or more importantly create a cavern under the concrete (can cause cracking).
wear safety goggles and be carefull if it's a real high pressure machine.....some of those can take off fingers
