The Italian's men slipped to third on the table after a 2-0 loss to Lille on Sunday, which came after a surprise loss to Reims in the Coupe de la Ligue.
Ranieri said his team needed to avoid concentrate lapses and wants them to develop a mentality which will make them more aggressive.
"I think what we need to change is our mentality. Reims and Lille played in a more aggressive approach than us," he said.
"Football in France is all about being aggressive. We have to understand that is very important to be aggressive, to play with an aggressive mentality."
Monaco face Evian TG on Friday with Pascal Dupraz's men in decent form having won consecutive league games to move clear of the relegation zone.
Ranieri is wary of an Evian side who can hurt his team on the counter-attack and pinpointed Modou Sougou as the main threat.
"Evian have reacted well. They have won their last three games. It's going to be a tough match. Like many games," Ranieri said.
"They defend well and they counter-attack with pace. Sougou for instance is very fast."
Ranieri expects Evian to test his side but believes Monaco will be good enough to deal with the threat if they are at their best and most determined.
"I want pressure because for me, it's important to play at 100 per cent level," he said.
"Like I said last year, every team will play at 120 per cent against us. I have a lot of good and technical players.
"But the most important thing is to focus on the league and to play with high determination."
