Parker... Great question, and one that you will (or should) constantly review in your head.
All of us want to maximize profits, have happy and repeat customers. Of course, those three things usually conflict, and make for a great argument going on in your head (and on an internet forum, or at a dinner table, or in a bar room.)
In my opinion, First, you've gotta create a enough business to make a living. Lower margins, more work. When you're starting off, that's probably what you've gotta do.
As business picks up, and you get more driveway jobs, and some other things that might pay better... you ease your prices up to suit your demands. No need to go do a discounted driveway when you have something better to do. Although, you can do a better job advertising (even for free) and actually charge more. (That's the goal in my biz.)
What margins are correct will depend on that old supply/demand thing. If there's plenty of commercial/industrial work in your area, a homeowner is going to have to pay more for your time.
Detective work in your area will determine your real answer.
The amount to charge is "what the market will bear." (and then make sure you made some money... if not... do something else!)
Good luck!!