With the right type of Jet you should be able to cut way the grass as you are cleaning, otherwise I would suggest you inform the customer that grass removal is extra; either use a Burner or scratch it out with a gardeners knife of use weed killer chemicals.
To remove the dirt I use a water vacumm and and suck it up with the excess water, then chuck it on the customes compost heap.
I think the Yellow pages would be good for this, bit expensive but i find quite effective. Also ask your new customers to pass on a recommendation to their friends.
Try canvassing, offer potential customers a demo area of their driveway, when they see the difference they cant say no.
Use laeflets with a before and after picture. More effective.