"It's pointless to look any further than [game] tomorrow. Maybe it's a trap we have fallen into in the past. When being ahead and feeling comfortable, [we] realized that some of this approach was not right. It's a different game tomorrow, We know how tough the opposition is, you can see how tight all of the knockout matches are," Southgate said.
When asked what he expects from Colombian side, Southgate explained that Colombia's tactics will depend on how much space will be available to them during the game.
"It will depend on how much space we will allow [Colombia]. The teams they faced gave them a different amount of space, and they played in different styles. They gave a very good performance in the game against Japan. And they punished Poland, when Poland gave them a lot of space. We have to make sure our work without the ball is spot on, because the Colombians can hurt you as a team. But that would be the same for every team we play at this stage of the competition. We want to control the game with possession as well. It's a very good test for our team," Southgate said.
England will face Colombia in Moscow on Tuesday.
The head coach continued speaking about the lineup for the upcoming game, namely his side's forward Raheem Sterling. Sterling started in two of England's group-stage matches, but failed to score.
"I have great belief in him [Sterling]. He's been a really important part of the team… His main key in movement is his ability to run at the team from the deep… I don't know why there has been such a focus on his position in the team and not on the others'… He's a player that we will be immensely looking forward to this occasion tomorrow," Southgate told journalists.
When he was asked if England were ready for the possible penalty shootout in the Colombia clash, he noted that the team has been "through various drills to prepare".
"They [the players] play delivery and technique, so, like all of the players, we've been through various drills to prepare, and once we get to that point [penalty shootout], we'll know our ranking of players… We're prepared, but there's a lot of football before that point, and the primary focus is preparing for what happens during the flow of the game. But should it come to that stage, we're ready," Southgate said.
It's Difficult to Stop England Forward Kane — Colombia Head Coach Pekerman
Meanwhile, addressing the upcoming game, Colombia head coach Jose Pekerman said on Monday that his players should pay extra attention to England striker Harry Kane as it is very difficult to stop him.
"Kane is a great, outstanding player. He had a remarkable season with Tottenham. He scores a lot and plays well. We should keep an eye on him. It is very difficult to stop such a striker," Pekerman told journalists.
England captain Kane scored 41 goals in 48 games for Spurs last season and has netted five goals at the World Cup so far, including a hat-trick in England's 6-1 drubbing of debutants Panama.
What concerns the Colombian lineup for the game, Pekerman expressed hope that James Rodriguez would be able to take part in the round of 16 match against England, as midfielders James Rodriguez and Miguel Borja were both training individually on Monday.
The Colombian team trained at the Spartak stadium in Tushino, north of Moscow. Rodriguez suffered an injury in the final match of the group stage against Senegal and was substituted in the 32nd minute of the match.