My normal washing routine is :
1.rinse car with cold water
2.wash with Mitt and two buckets of water, one soapy (with proper car shampoo,never fairy liquid.One with clean water to dip mitt after each stroke.
3. rinse with hose on steady stream to let water sheet off the car
4.dry with waffle weave towel (never use a chamios - they're not designed for drying cars,they're designed for windows)
I'd also think about claying the car regardless of age-the secret of a good finish is good prep.