Do take a quality tent with a rain fly. Expect rain when camping in Europe. Sure, you only need a two-person tent, but when it rains you'll want room to move about. Things like getting dressed and playing cards or scrabble are tough to do in a two-person tent.
Don't move too often: Choose central locations with day-trip possibilities and stay at least three days.
Do plan some hotel or pension stays, particularly on travel days. It is easier to have a room waiting for you.
Don't expect to see as much as if you were staying in hotels: Camping takes extra time; with setup, breakdown, shopping and laundry there is a lot to do.
Do budget between $100 and $200/day for two people. At $100/day (our budget which included everything except airfare) a couple can live quite well. $150/day means lunch out and other extras. At $200/day, by camping standards, you're royalty!
Don't plan scenic drives or day-trips on moving days unless you have planned for a first night hotel at your next destination. With campsite breakdown, the drive to your next stop, meals, finding a campground you like and setting up, you'll have a full day.
Do have a rewarding and affordable vacation. Happy camping!