Parallel parking comes down to two simple things: patience and confidence.
Patience is especially important when you are parking on a crowded street with other cars waiting behind you. This is when you have to block them out and focus on the task at hand, which requires confidence. This confidence comes from knowing just how big your car is and that it will fit in the space you are trying to park in. As soon as you have the patience and confidence down, the rest is easy.
Once you have found a parking spot, use your turn signal to indicate that you are about to park in the space. Pull your car forward until you have pulled up beside the car you are going to parallel park behind. Your rear bumper should be even with the rear bumper of the car next to you. There should only be about two feet of space between you and the car next to you. A good way to gauge two feet is that you should feel like your side-view mirror is almost touching the car next to you.
Once you are aligned with the car next to you, put your car in reverse and start to back up slowly. Although some people use their side mirror to help guide them, it is always best to just turn your neck around and see for yourself exactly where your car is going. As soon as the car starts moving, turn your steering wheel as far as it will go toward the curb. Once the back of your car's front door is even with the rear bumper of the car beside you, begin turning the steering wheel away from the curb. As you continue backing into the parking space, keep turning the steering wheel away from the curb until you are in the space. Remember that as you are backing in, the closer your front fender is to the rear bumper of the car in front of you, the closer you will be to the curb.
Once in the parking spot, straighten out the steering wheel and pull forward or backward in the space as needed to center yourself. At this point your car should be six to eight inches from the curb.
If you are parking on a downward hill, make sure to turn your wheels toward the sidewalk, and if parking on an upward hill, make sure to curb your wheel away from the sidewalk.