The Italy international will be key for Massimiliano Allegri's side as they look to hold onto their two-goal lead from the first leg, and he admitted they will try to impose their own style of play on the game.
"Our coach prepared us very well for this match. He told us not to be hasty, to be patient and wait for the right moment," he told Sky Sport Italia.
"We studied Barcelona, and we must limit them as much as possible and then pick the time to counter-attack.
"The important thing is to play without pressure and be aware that we too can have our say. Milan have quality players and we could also impose our style on them, if we wanted to."
The lifelong Rossoneri fan has been in superb form for the Italian giants this season, and he admitted the 2-0 first leg win at San Siro will go down as one of his most memorable nights on a football pitch.
"It was an unforgettable night that I will carry in my heart for all of my life. It was amazing right from the moment the fans greeted us outside the San Siro garage and playing in a packed stadium gives you such a buzz," he continued.
"We needed to sacrifice ourselves and work hard against Barcelona, as we knew their characteristics. I think [Kevin] Prince Boateng and I did really well that night."
The Rossoneri have turned their season around in recent months, and after a poor start to the campaign now find themselves third in Serie A.
El Shaarawy puts the upturn in fortunes down to coach Massimiliano Allegri and admitted he wants to stay at the club for the foreseeable future.
He added: "The team has always been united and never gave up. The coach was close to us and we were close to him. Massimiliano Allegri was our strength. We started the campaign with so many problems and the only way out of it was to stay united. Now we must continue on this track.
"I have great respect for Allegri, as he has done so much for this team. I hope he can remain with us and with Milan."My objective is to stay at Milan for as long as possible, as this is the team I have always supported. The captain’s armband? I’m not thinking about that right now."