Two ways I plan to use: Getting stat additions by a random percentage, for example, fighting weak enemies means you have a 10% chance of getting stronger upon defeating an enemy, while fighting enemies stronger than you raises that chance, say something like 30 to 50%, based on how great your stat total is compared to the enemy.
Another is a system that determines if your play was skilled and intuitive. If you just spam the same attack over, and over, the amount of stat growth you receive is small, say +1-2, while winning a fight skillfully, via use of techniques, wether you outwitted your opponent, or made a turnabout of the fight and so on, will net you +12 to 24, based on an algorithm. There would be a bonus as well in this example if your opponent is stronger than you.
Thus, if the system detects that your opponent stood there without fighting back and you are lower level, it would net you +1, since it detected your amateurish skills and that you defeated somebody stronger than you with no effort as they never fought back.
This would prevent people from fishing and so on to unfairly gain stats.