If you've played the Punch-Out!! games enough, you've probably gotten the basic strategy down of Dodge Punch, Throw Punch. Which is great for most situations, but when you're ready to step up your game you need to master the art of counterpunching.
Throwing a counter-punch is easy... in concept. All you have to do is wait for your opponent to throw a punch
Then counter with the same punch on the same side (i.e. if he throws a Left Jab (your right) you counter with a Right Jab)
Done right he'll be stunned and ripe for a few more punches
So you can unload a little more.
Master this technique and you can shave precious seconds off your KO time in Time Trial mode, which is great, but you can also completely destroy the computer opponents and show off to your friends, which is really what Super Punch-Out!! is all about.