practice makes perfect, summer is here so try a couple methods. and i can't rave enough about zaino for a black car

 

When I worked at Nissan, we would get these really sad looking z's on trade ins. I was taught to use Mineral of spirits all over the car (in the shade only) for 5 minutes we would rub it in. Then wash it off with soap and water. The car was stripped of all kinds of sh*t (old wax, bugs,etc..). Then we would buff the hell out of it. The cars turned out new like. Good luck