Advice for any Street Fighter game, not specific to Super Street fighter 3D:
Block. You only lose a round if your adversary deals damage to you, so every loss is due to a breach on your defense.
Don't jump very often. Jumps have predefined arcs and you can't block during a jump. So, it's easy for your adversary to predict where you'll be during a jump and attack for free.
Every attack takes some time to land. If your adversary uses a faster attack before your attack lands, you will take damage.
If you miss an attack, there is some time for the recovery. If your opponent attacks you during this period, you can't react.
So, the safest way to play is to stay on the defensive and attack with quick moves, punishing your opponent when they make a mistake.
Supposing you're playing Ken vs Guile. A Shoryuken is a good anti-air move. But if you misjudge the distance, it will whiff, and it has a huge recovery time, on which Guile may hit you with an Ultra or another dangerous move. So, you could consider using a High Kick or a crouching High Punch, since those moves are faster (but not completely safe if you miss either).
Long story short: defense is safer than offense, at least before you learn how to attack well. Block your opponent's attacks and punish them on their mistakes. And never jump if Guile is crouching.