England coach Duncan Fletcher said his team must keep working, despite their triangular series triumph down under.
Fletcher's team recovered well from some fierce criticism
After five defeats in the first six matches, England won four games in a row to win the final against Australia.
"We've got to be very careful, a young side will have ups and downs," he said. "Consistency comes in experienced sides who've won from difficult situations.
"There is a huge improvement to make, but if they can make that improvement they'll be very, very competitive."
Fletcher, who took over at the England helm in 1999, re-iterated that he would consider his future after the World Cup finishes in April.
"From my point of view I've got the self-belief and the support of the players and that gives you the confidence that you can carry on with the job," he said.
"I wouldn't like to ever say which was the best time, there have been some great times with England, and this must rate in the top 10," Fletcher said.
"Winning the Ashes was tremendous but to beat them in one-day cricket, where we haven't played well, in their back yard, is a tremendous achievement."
It's nice to see we've got people like Vaughan and Pietersen we can bring in but we've also had guys who have put in some great performances
The 58-year-old was cautious about his team's chances in the World Cup, where they face Canada, Kenya and New Zealand in their qualifying group.
"On this tour I thought we were a year away but a young side can bring that forward to six months," he said.
"This side has brought it forward probably to three months and there's a very good chance they've brought it forward to a couple of weeks before we go to the World Cup."
On the question of team selection and how the current side will fare when established players return from injury, Fletcher said: "These guys have done very well so where do you go from here?
"There are quality players to bring back, especially Michael Vaughan as captain, he's done a good job for us, he's a good opening bat and always played well against Australia and Kevin Pietersen is world class.
"It's nice to see we've got people like that we can bring in but we've also had guys who have put in some great performances out here.
"It has given the guys a lot of self belief but all the time you have to drive yourself to come up with new ideas and we have to believe there is no complacency.
"They are very receptive and I'm sure they will listen to us."
England name their 15-man World Cup squad on Wednesday.
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