Mike Catt told The Rugby Club that England want to have a clear idea of their 2015 World Cup squad by the culmination of next summer's tour to New Zealand.
Stuart Lancaster's charges won both of their Test matches in Argentina earlier this year and will hope to further nourish their side in the upcoming Autumn Internationals as well as in the Six Nations.
England's attacking skills coach Catt - part of his nation's 2003 World Cup-winning team - hopes the Twickenham troop have ironed out any deficiencies in their game once they have locked horns with the All Blacks in just under a year's time.
But the former Bath and London Irish centre says there are still plenty of places up for grabs in the England party and warned players already established in the set-up that they will have to maintain their standards to keep their spots.
"We need to make all our mistakes by the end of the New Zealand tour so that we have learnt our lessons, know how to beat the best in the world and have players cemented in," said the South African-born star.
"The Lions guys and the guys that went to Argentina and did well in the last Six Nations have a lot of credit in the bank so that will be taken into account - but they have to be on top of their game.
"We have a large amount of competition in each position - and every position is up for grabs."
England took a fairly inexperienced party to Argentina this summer with some of their star names playing in the British and Irish Lions' successful tour of Australia.
Worcester flanker Matt Kvesic, Bath centre Kyle Eastmond and London Irish wing Marland Yarde all boarded the plane, and Catt says the South American sojourn was a positive experience for him, too, as he was fully able to gauge the quality of the players involved.
While England were prospering in Salta and Buenos Aires, their more youthful countrymen were winning the sixth annual IRB Junior World Championships in France, leaving the game on these shores in a seemingly promising state.
However, Exeter coach Rob Baxter - who managed England's forwards during the trip to Argentina - says it could be a mistake if Lancaster included a host of rugby union starlets in his squad for the World Cup on home soil in 2015.
Catt said: "As a coach you have a preconceived perception of a certain player before you work with them, but what I found on the Argentina tour was that until you work with somebody you don't actually know how good they are."
Baxter added: "You want to drive a culture where it really means something to pull on an England shirt, but there is a fine balance between development and making sure you are picking the best players.
"As much as people like to say the teams that get it right are the ones that plan ahead and see the future, if you look at the World Cup-winning teams, I wouldn't say too many of them have had periods running into the World Cup where they have been experimenting."
To hear more from Catt, as well the thoughts of Gloucester's Freddie Burns and England coach Lancaster, hit the video above.