2.Experience.

When Cristiano Ronaldo first burst onto the scene, he was a flashy, out and out winger, who liked to cut inside, beat defenders at will and score spectacular goals. That was the qualities that caught Sir Alex's attention and he brought Ronaldo to Manchester United to provide a solid platform to showcase to his talent to the world. Same was the case with Messi, who too liked to take mazy dribbling runs and score spectacular goals.
But as time went by, and they get more matured and experienced, they both opted for a slightly subdued, yet effective approach. Ronaldo, in particular, knows his weaknesses as a player, that he can't dribble the way he used to. So, instead of attempting fancy dribbles and stepovers, he turned himself into a prolific marksman, one who uses his off the ball intelligence and his finishing abilities to great effect. He started to pass a lot more than his Manchester days and his link-up play with his teammates has improved a lot too.
Messi too, on the other hand, understood his role in the team as a chance creator since the departure of Xavi left Barcelona's midfield short of creative ideas. So often we see Messi dropping deep to pick up the ball and create chances for himself as well as his teammates, something which was seen to a lesser extent during his time with Xavi since there was no need for it back then.
As both of them got more experienced, they understood their importance to the team and thus, molded themselves as per the needs of the team, which has reaped handsome rewards for themselves as well their respective teams.