I learned by placing cones around so I would know how to do it for my test and so if I hit something, it wasn't a big deal. I made the space smaller than I should've, but I was able to park within it so parking in an area bigger was no problem.
Well, first, do you want to do it in one fluid motion, or do you mind stopping every so often. The second method is good for learning and eventually you will get the fluid motion.
First, pull up next to the car. I would have my mirror be in line where their steering wheel, it may be different for your car though.
Put the car in reverse and back up about two feet or so. Stop. Look back and see if your back, right wheel is next too / slightly behind their rear tire. You will be more or less pivoting on the back right wheel, so being too far forward can result in hitting their car.
Turn the wheel to the right as far as it will go. Then back up into the spot. Stop when your car is about halfway into the spot or at about a 40-45 degrees with the curb. If you hit the curb with your back wheel, you've backed up too far. Just shift into drive and pull forward a few feet and then shift back into reverse. You will be pivoting on the back, left wheel, so if it is not in line with the wheel of the car behind you or it looks far out of the spot, you will be far out of the spot. Or, if the wheel is really close to the curb, you will hit the curb. Adjust accordingly before continuing. If you will be far out of the spot, you can adjust by turning the wheel completely to the left and then turning back towards the right a bit, though it may be easier just to back up a few inches.
Slowly back into the spot. Your front wheels will swing into the spot as the car goes back a little bit.
If you worry that you are going to hit something, park, get out and check. The more you turn to the right, the more your car will roll back instead of swinging the front. If the front of your car is in the spot, stop and straighten out the wheel. Stay at least this far back in the spot so you can pull out of the spot easily. If you pull too far forward, a car parking behind your might block you in.
For a more fluid move, you do all this without stopping in between and turn the wheel while backing up slowly. When doing it fluidly, consider that you will continue to roll back as you turn, so you can turn a second or two sooner than you would the other way. Also, when you turn back to the left, you may hit the curb doing it fluidly unless you turn the wheel kinda fast because your car will continue backing up as you turn, so keep that in mind and either slowly down more or turn the wheel faster.
Going slowly is the best advice I can give you. If you can tell me which part you are having the most trouble with, I can try to give a better idea of what might help you.