There are a couple threads that started to go off topic about this so I decided to start a new thread solely for this.
First tip I'd like to give people is right off at the start of a match run in a circle around your opponent while he shoots off some of his super powers draining his meter, then go in for the kill.
Use the environment to your advantage. Most characters don't like being hit by cars. Try to ring out when possible (The bridge, Daily Bugle, Grand Central), which is actually pretty easy to do using your throws. In the power plant stage destroy the electric pillar because it will affect you more than your opponent.
I've found that the computer has a harder time blocking your attacks if you lead with a normal punch first. So tap punch once then hold down the R button and repeatedly tap punch again to go into your special move. Also lead with a punch before trying to throw or just run past him and turn quickly to throw.
When using cards get the maximum effect. Use four cards of the same color to get synergy bonuses. Make sure one card is a health gainer. Either one really big boost like Uber3 (+50 HP, +15 Rage, +10 PP) or one that recharges and can be used multiple times like my fave Ignore Injury (+15 HP, recharge every 20 sec.) Also one good rechargable attack card like Uber2 (+8 to all attacks, recharges every 25 sec.) can really rip into your opponent. I personally don't like the armor bonus cards.
To enhance play a bit try using all 4 character cards together for each character. You will get a synergy bonus and be able to use each guy to maximum potential.
Learn to effectively kick guys on the ground. If done right you can just keep hitting them until they die.
Every opponent has a weakness. Find it and exploit it.
I guess that's enough for now.