When I train my team, I make sure to EV train (Raising effort values) them too. EVs are surprisingly very important to a pokemon’s stats, and can raise or lower if you train against certain pokemon, use items on them, have your pokemon get pokerus, give them held items, feed them a certain berry, etc.
In the genV games, an experience share is fine to use for leveling up, unlike the generations below it, where the pokemon that didn’t defeat whatever pokemon you were fighting don’t get EVs if they level up in that battle.
Keeping track of EVs can be time consuming, but it’s very much worth it. When EV training, I tend to have the pokemon that I’m training hold the macho brace and have (or have had, if pokerus is away, it still affects the pokemon, it’s just not contagious to the rest of the team anymore) pokerus and battle pokemon that raise the EVs for a specific stat the most.
If you do so, but still find your pokemon fainting all of the time, try tweaking the moveset. Putting a useful strategy that you would prefer into a pokemon’s moves really helps too. Use the strategy you like best and that fits with the the type of team that you’re making. Another thing with moves is using attack and special attack moves properly if you want to hit hard.
For example, if I have a venusaur, which typically has a higher special attack stat than it does attack and I’ve raised it’s special attack EVs to their highest, it would be a better choice to have it know a special attack move of one of it’s types (For STAB) if I want it to hit hard. Petal Dance, a special attack move would be one optional choice.
EVs aren’t the only values to pay attention to, by the way. IVs are also very important too… but it seems as if I’ve covered a lot already. |D Time to take a break from typing so much.