There are a few battles during the World Martial Arts Tournament. The battles are always ordered randomly, and not all characters can be battled each time. You'll probably have to play through this part of the game a few times to battle everyone.
By the time you reach this battle, you should have a higher HP and Ki number. Yamcha also has a lower Ki number than Clone Goku, so this battle shouldn't be too hard. Just keep using Ki attacks to weaken him quicker. Otherwise, use the same strategy as you did with Clone Goku. This isn't a big battle, and probably even similar to the practice battle itself. Also, his physical Ki attacks can be blocked more easily than his physical attacks. Since he always uses his special Ki attacks, most of his attacks can easily be blocked.
Tien is probably the easiest battle out of all other characters in the World Martial Arts Tournament. His high HP and high Ki number (even if you verse Tien the second time instead of the first, it's not possible to get 36 Ki by this point—the maximum is probably 34) may be intimidating, but the battle can be quite easy if you minimize your physical attacks and try fitting in as many Ki attacks as possible. If you have enough Ki in the end, finish him off with a Kamehameha. By the end of this battle, you should have a new physical Ki attack, the headbutt. This will prove much more effective than the originally unlocked physical Ki attack, the throw.
Chi-Chi can be an easy opponent if you have a strategy to back you up. Try making frequent patterns of physical attack, Ki attack, physical attack, Ki attack, etc. Throw your own moves into the mix, and maybe make a few movements. Remember, the closer you are, the more damage your opponent takes. Two out of four of your moves Chi-Chi will successfully block. This can get annoying, but be patient and you'll get to zero quickly.
Probably the most challenging opponent in the World Martial Arts Tournament is Krillin. This battle can be good practice for tougher battles, so try practicing various strategies here. No matter how hard this battle may be, it'll be almost impossible for Krillin to take you down, as you should have at least 300 HP by this point. Using Kaio-Ken in this battle would also be a safe option—the stronger you are, the easier it'll be to block Krillin's attacks.