Leonardo would like his Inter side to show greater concentration and avoid letting in silly goals.
The Nerazzurri have won each of their three games under his management, but not one of those victories have been accompanied by a clean sheet.
Speaking ahead of this weekend's match against Bologna, Leonardo said: "The first games have given us confidence, but Bologna are in good shape and we must be careful.
"We concede avoidable goals. We must improve."
Asked about reports linking Sulley Muntari with a move away from the club, Leonardo said: "He must decide what he wants to do.
"Today Muntari is an Inter player and there is no alarm. If he stays, he'll stay with a lot of desire to do well."
Finally Leonardo had praise for Inter captain Javier Zanetti who will make his 519th appearance for the club in Serie A this weekend.
"The consistency. The way in which Zanetti plays the games. It's incredible. He is someone to study.
"Javier is a legend. His stamina and ability to recover in time for games is impressive. His is a beautiful story."