I placed 1st in the T5 nationals of my country, and placed 2nd in the T6 nationals. I know how to play this game.
I'll add info to the first post as I feel like it.
The guide Aris posted on his website is good but I want to look at it from a different approach of understanding the principles behind the game aka what happens when all the rules connect together aka the bigger picture.
Golden rule #1-
When in doubt, block high. Which means you'll be blocking high most of the time. If you think you know what the opponent is going to do, do the solution for it. You don't need to actually remember frames. You just remember how the move looks like, and what move deals with it.
Golden rule #2-
Everything comes down to risk/reward ratio. That is also the reason for rule #1, since mid attacks are low risk high reward, and low attacks are higher risk lower reward.
To compare to 2D games, you poke poke poke(=3D mid), and to keep them honest you mix in a walk up throw once in a while.(=3D lows)
Golden rule #3-
The flow of the game is usually "I attack, then you attack, then I attack again" so all you need to think about is the opponent's next move. There's less emphasis on overall situation in the match, because one good prediction is all you need to turn the tables. That is why at the highest levels of play, you also see fewer launchers and big moves. People mostly play with the smallest, safest pokes, exactly because they require more effort and prediction from the opponent to be punished.
Golden rule #4-
Don't be impulsive after a knockdown. It's easy to abuse someone who tries to rollback/get up/whatever the 1st chance he gets. Try staying on the floor and mix not just "how" you get up but also "when". Also, eating a hit on the ground allows you to get up safely after it, and escape from a scary mixup on wakeup, so it's a nice sacrifice to consider.
Golden rule #5-
Don't expect to NOT get random'ed out in tournaments. In 2D games you can "do your thing" easier and you don't need to have matchup knowledge to deal with simple scrubs. Not so much in Tekken. You'll eat random shit and lose to moves just because you are not used to seeing them.
So let's say you played some casuals vs a Christie player and lost horribly. You go back to training mode and let the CPU do the moves he used. You learn how to block them, and look for holes. (punishable on block? easily parried? can be side stepped? can stuff an attack in the middle of the string? can duck the 2nd hit? etc. etc.)
So focus on learning the game one opponent character at a time.