#2 Play a high-pressure game
"In my teams, the goalie is the first attacker, and the striker the first defender." - Johan Cruyff
The biggest mistake Barcelona made at Parc des Princes is that they gave the PSG players a lot of space. Verratti, Rabiot and Matuidi dominated the midfield while Di Maria and Draxler ran past the full-backs with ease.
Barcelona need to put more pressure when PSG are on the ball and make sure that everyone is marked all the time. Staying back and defending is something they should avoid at all costs.
Messi, Neymar and Suarez have to contribute defensively by putting pressure on the PSG defenders as soon as they get the ball, and the defenders should play a high line tonight. Meunier and Kurzawa were dominant against MSN in the first leg and that's something they should avoid.