Three Tips:
1. Get Your Stamina Up, It'll Help.
2. If Your on A Losing Streak And Your Stamina's Not Very Good, Use Your Boxers Speed/Power To Your Advantage, E.g Power Use It To Break Their Guard Or Bring Their Guard Down By Throw Body Shots. Speed, If Your Losing A Fight, Say Its 5th Round Throw Everything At Them Keep Hitting Combo's Even If Your "Yellow Bar" Goes All The Way Down Don't Stop Until You Do A Enough Damage.
3. Use Your Guard Respectivly, Try And Parry Them.
These Are My Idea's Sorry If They Don't Work Like I Say They Do.