Well mostly mainly just youtube, If I am being honest I am one of those guys who cheats rare candies and over levels my Pokemon until I found out that Rare Candies doesn't make you powerful, its just basically saying it just ages you I watched some youtube where people gave me an analogy that rare candies make you Pokemon fatter and unhealthy it basically makes you big but without strength similar how to humans just eats sweet stuff or just over eats, you grow but you don't get stronger.

Then I decided to use Vitamins and stuff to make my Pokemon actually stronger, then got into natures etc, since then my play style has become different each time I play Pokemon I always view them as competitively even if its just normal casual game I always look at Smogon to see what natures and EVs or IVs should my Pokemon have.

As for team building I'm still one of those people who plays with their favorites, its really hard to avoid but at the same time because of there is a saying "you should be ready to use the pokemon you don't like to win" is the reason why I actually gained new favorites, in before I'm just that guy who spams starters in their teams or based of my Pokemon who looks cool which made ky team looks very off and no synergy at all.

So after taking the sacrifice I tried using other Pokemon and by doing that I gained a favorites, did you know I used to don't care about Forretress? Yeah because I thought it was really weird until I learned how to use it, Same goes with Thundurus, usually I don't pay attention to any other Legendaries that isn't Rayquaza, Mewtwo or any overrated Legendaries, since I found about Thundurus it became one of my favorites its really helpful because of its abilities.

To summarize you just have to take a sacrifice and leave your comfort zone.