Here is what you do.
you need
1. pinstripe tape (same stuff at autozone or oriellys)
2. blue painters tape (both 1/2" and 1" size)
3.
n number of drop clothes to reduce over spray on the car
4. razor blade
5. heat gun
6. mircofiber cloth
7. plasti-dip
Once you have all of those items, plan out what kind of design you want. Use the pinstripe kit to mark off your design. the pinstripe is going to give you the sharp line that you are looking for. once you have your design use your 1/2" painters tape to mark where the stripe or boarder is going to be laid down. once you laid the 1/2" down go back over with the 1" to help give the area you dont want painted.
Once you have the lines down use the razor blade to cut the tape at the door jams and the hood etc. Use the drop clothes to help reduce the amount of over spray. Lay the desired color dip down. let it dry for an hour. Once it is dry, take everything off accept the 1/2" tape and the pinstripe. Here is where you get the sharp lines. With everything clear, go over the dip with the heat gun
while pulling the 1/2" tape off and the pinstripe. be careful not to stay in one spot or you will cause the dip to strink. All you are doing is making the dip hot enough so you can "rip" it apart. While lifting the tape in the direction you are moving, use the heat gun to help the dip stay on the car in a fluid back and forth motion. I also moved with the tape while it was coming off of the car. If the dip does have an imperfection or two go back over it with the heat gun and used the microfiber to dab it back down. do this at the same time.