I've been inline skating since I was about 5 years old. Not
exactly rollerskating, but pretty much the next closest thing (unless you actually mean rollerskating, in which case, awesome).
Here are the two biggest things beginners don't usually get which are imperative to learning to skate.
1) Do NOT lock up you legs or keep them stiff. It will be scary at first and you will almost certainly fall, but do your best to keep your knee, hip, and ankle joints loose, yet still firm enough that you don't flop to the ground (duh). The faster you go, the more you crouch down. Stay loose, my friend.
2) Your balance should NOT come from your waist up. In general, yes, a lot of your balance does come from your torso. But that's mostly passive balance. What I'm talking about is active balance - that is, shifting your weight. Shifting your torso will cause you to fall over far more because you're shifting your entire center of gravity. Most of the time you will end up overshooting and falling on your butt. Instead, balance from your hips down. This is done less by shifting your center of gravity and more by adjust your leg and joint positions. Even a slight adjustment in one ankle can make or break your balance, but it's far easier to control a small ankle movement instead of trying to adjust more than 50% of your body weight.
Both of these things should be practiced in combination. Once you've gotten a bit better at that, consider moving on to some of the below exercises.
- Balance on one foot for as long as you can (both moving and stationary).
- Simply try to walk/jog around in the skates on a variety of surfaces. A large part of learning to skate is about becoming "one" with the skates.
- Once you're a bit more confident, setup a slalom course. As you get more confortable, shorten the distance between each cone (or whatever you're using) and speed up a bit.
- I also strongly suggest learning how to stop properly - both with the brake and with another method (possibly a turn-stop). Remember, grass will not always be there for you to land on, and I don't think running into cars is too comfortable either. ;)
Hope you can get something out of this. Keep on skatin'.