Better created character
When creating a character, set his heart, power, and speed high. It is important to have the heart to be high. If you jab a lot then throw a punch, it will work much better than just bashing the buttons.
When you get to the screen to set your stats, choose "Heavyweight" then select a height of 6'0" to 6'3" and weight of 200 to 210 lb. Then work on the stats. The most important ones are speed, stamina, heart, and power. Go as high as you can so you can give some and take some hits.
Easy Knockout
When creating a boxer, give him a the Body Blaster as his special move. During the match, throw a few jabs and back away. Wait for your opponent to move in and hit him with the Body Blaster. It should stun him. Hit him with it again. Continue to do this and you will knock him out in no time. This can be done in all three weight divisions and works almost all of the time. Also, if you find yourself in trouble, try the Backhand (elbow) followed by the Body Blaster. It either takes off a good amount of energy or stuns them, leaving them open for the Body Blaster.
Easy Win
After completing the game you will be prompted to select a cheat. Choose teleportation. You will have to press your special and R to use it. If you are playing two player or exhibition mode, set the match to one round. Hit your opponent a few times then keep teleporting for the rest of the round and you will win.
When creating a boxer, give him a the Body Blaster as his special move. During the match, throw a few jabs and back away. Wait for your opponent to move in and hit him with the Body Blaster. It should stun him. Hit him with it again. Continue to do this and you will knock him out in no time. This can be done in all three weight divisions and works almost all of the time. Also, if you find yourself in trouble, try the Backhand (elbow) followed by the Body Blaster. It either takes off a good amount of energy or stuns them, leaving them open for the Body Blaster.
When creating a new boxer, select the Cake Mixer as his special hit combo. When your opponent is about to get knocked down, hit him with the Cake Mixer. About 90% of the time, he will do a spin in the air and fall to the mat.
When creating a new boxer, select Macho as his special hit combo and set your speed and power stats up. Throughout the fight, keep using the special. The combo is so quick your opponent cannot react to it, giving your an easy win.
Unlock Cheats
To unlock cheats beat the game in career mode. After you beat Muhammed Ali fight 3 other fighters that want to challenge you. If you beat all three a list of cheats will pop up. Pick one cheat and it will be added to your list. When you do this your boxer will retire and you'll have to start all over again. Do this repeatedly to unlock more and more cheats.
Better created character...