Basics (All characters):
Guard Impact:
Guard Impact is a very useful technique. To use it, all you have to do is press 6g or 4g. Well, it's a bit harder then that. GI actually knocks back your opponents attack, leaving them open for you to do your own attack. Then, there only option will be to attempt to guard impact your attack. It requires a very careful timing (You must GI a split second before their attack hits you).
It's best to use GI when your opponent starts repeating attacks or you know what your opponents next attack is, or else don't go out of the way to do it. 6g GI's high and med attacks, while 4g GI's med and low attacks.
And remember, you don't always have to attack after a GI. You can 8 way run, catch them off guard when they try to GI your attack (You know, that attack you never made). There's tons of different things you could do. :)
8-Way Run:
Moving in any direction activates 8-way run. That's what special about the movement in SC, you aren't limited to just side-stepping. With 8-way run, you can move any direction. There are also various attacks you can do only while moving in a certain direction. Up causes you to start moving away from the screen, while down moves you towards the screen (Jump is 8g and crouch is 2g). 8 way run is very useful, and you'll get the hang of it very quickly.
Air Control:
When thrown into the air, opponents can strike you a couple of time while you are falling back down, or "juggle" you. To avoid painful juggles, it's usually a good choice to use air-control. By moving the control stick in any direction, your character will move that way while trying to land (Works the same way as 8-way run) and you can get back to ground safer.
Ground Control:
When on the ground, simply pressing up or down on the control stick will cause your character to roll over (And, eventually get back up). This can save you from getting hurt from your opponent attacking you when your down, or using his "wake up" moves on you.
Attacks:
There's a rule to the attacks that you would do well to remember. Side-stepping beats vertical attacks, Vertical attacks beat horizontal attacks (And crouching), Horizontal attacks beat side-stepping, and crouching beats horizontal attacks. :)
Throws:
Throws are some of the most powerful moves in the game. To execute one, simply press g+a or g+b. These throws can be cancelled if you opponent presses the same button continously at the beginning of the throw. If you execute a throw when your opponents back is turned, then he/she cannot cancel/block that throw, and there are other throws (Character specific) that are unblockable.
Unblockables/Guard Breaks:
There a some moves (Different for each character) that cause your opponents guard to fail momentarily or that are simply unblockable. GB moves glow blue, and unblockables glow red and usually require a SC or automatically charge before the attack. Unblockables are usually slow, but if you watch out for the opportunity to use them, it'll be killer. :)