I'm about 2 for 25 right now in ranked. And one of those two wins was against someone who was afk (afc?).
I'm far from an expert, and I actually consider myself somewhat an average player, so take it for what it's worth. Here are some tips that I've received and that I've figured out over my causal stints:
1. Visit Tekken Zaibatsu, where they have specialized character threads. Tekken notation and lingo can be pretty frustrating to understand, but there are lot of good nuggets in the thread. If you're lucky, there will be a "Top 10 Move" character thread ... which is a thread where players post what they consider their Top 10 moves for that character. That should give you a baseline on which moves you should be abusing.
2. Listening to RIP give beginner advice in 1st Attack, find a reliable mid and reliable low for you character.
3. Again, per RIP's advice, movement is a critical component to success. I believe Avoiding the Puddle has a good tutorial. This is one aspect that I still need to greatly improve on.
4. Keep It Simple (Juggles that is). Rather trying to pull of max juggle damage that you can only pull off one out of five times, be satisfied with juggles that lead to solid damage and are easier and less flashy to pull off. Go for the complex stuff later once you've nailed down your character.
5. Abuse Your Opponent. It sounds sorta messed up, but if a certain attack works on your opponent, keep doing it over and over until he/she proves otherwise. If your objective is to win, this what you ought to be doing. If your objective is to learn your character on the fly and gain experience, then don't be so hard on yourself.