Stuart Lancaster hailed his young guns for their record win over Fiji, but admitted England will have to up their game for the arrival of Australia, South Africa and New Zealand over the next month.
Lancaster named an inexperienced team that contained 11 players with 13 caps or less, but they ran in seven tries to complete a steady 54-12 win over the minnows at Twickenham.
"Next week and the week after and the week after that we are going to have to be more clinical," Lancaster said. "It was good to get the win. We struggled a bit for 10-15 minutes."
He added: "We didn't convert every opportunity but we were pleased with the opportunities we did take. It was a good start but we recognised the quality of the opposition that is coming around the corner. We will have to step up a couple of levels next week.
"Our cohesion is growing and that is what we will need. Australia, South Africa and New Zealand are cohesive and organised, and we will have to be at our best."
Alex Goode excelled at full-back, offering England an effective second play-making option and broadening their attacking game, while Charlie Sharples was unfortunate not to score a hat-trick.
The Gloucester wing, starting in place of the suspended Chris Ashton, scored twice while Ugo Monye on the opposite wing bagged a try on his return to the England team.
Ashton is set to return to face Australia next week, giving Lancaster a selection headache which he welcomes.
"Chris Ashton is back so there are selection decisions to be made. It's not a nightmare at all," Lancaster said. "It's a great position to be in. Charlie did what we wanted him to. He was excellent in every area.
"We will now have a long conversation about selection next week. Alex played like he does for Saracens, he was excellent under the high ball, his ability to move the ball around. It was nice for Alex. He did well in the third Test in South Africa and he has maintained that form."