A little question /vp/

I have noticed that in every fucking game I play, every one in my party is heavenly underleveled in some matches (like E4 or post game things, even some rival battles), even if I battled every single trainer in each route.

It may sound retard but how I can fix this? What you guys do in order to get a good pokemon level team and not abuse items? Do you have already what team you will be having pre-game and only rush them? Any stupid strategy?

>inb4 caring about ingame shit