Coast while skating
In order to keep your speed under control, you need coast while skating. You can glide for a small distance and then speed up on your roller blades to be in control. Make a pattern such pushing off on rollerblades then time and in the end glide.
You need to apply break in case you are in a very high speed and about to lose control. You can do this by first bending your knees and then extend toe up which will lead in touching breaks on ground. Remember that it will take few seconds before you slow down so be patient. You need to lean your upper body forward in order to maintain good balance. In case you are still rollerblading very fast, you need to add more pressure on the brakes.
In case you are going downhill, you need to use T-stop while you are coasting. You need to make a solid base stance. In order to use the T-stop, you need to place one rollerblade behind the other in a way it makes 90 degrees angle. By this, the stopping rollerblade blades will drag along the ground, eventually slowing you down. Remember to place your stronger and more natural foot behind. In order to add more pressure, you can push down more along with extending of your braking foot.
You can always do figure-8s in order to slow down while rollerblading down a steep hill. In order to turn right, you need to move your right rollerblade slightly ahead of the other along with bending your knees. When the rollerblades are perpendicular, you need to switch sides. You can do this by putting your left rollerblade slightly ahead. Remember that you might lose control while doing figure-8s but this can control your speed while moving down the hill.