Former British & Irish Lions captain Brian O'Driscoll says the 2009 tourists must learn "huge lessons" from the trip of New Zealand in 2005.
The Lions, who will name their head coach for their South Africa tour on 14 May, lost the Test series 3-0.
"In 2005, the coaching staff went in with pre-conceived ideas as to what the Test team would be," said O'Driscoll.
"Not everyone performed the way they should have but some guys still got into the team."
The 2005 Lions were coached by Sir Clive Woodward, who had led England to World Cup glory two years before.
He took a huge party of 51 players and 26 backroom staff, but some players did not get a look in, creating divisions within the camp.
"It is the guys who are playing well when you are on tour who should play the Test rugby"
"If you play well you get selected next time round, irrespective of reputation or whether you have been on other Lions tours or whether you have been captain of your country. None of that should matter," said the Ireland captain.
"It is the guys who are playing well when you are on tour who should play the Test rugby. You have to give everyone equal opportunity to get into the Test team."
England World Cup winner Jason Robinson, who went on two Lions tours, said the large size of the party created problems in New Zealand.
"The more people you have there, the more people will be disappointed when the team is chosen," he said.
"Everybody who goes out there wants to play. If you are not picked for two or three games you are called the driftwood and you feel like that. It is important to get the numbers right."
Robinson also backed his former Wigan rugby league team-mate Shaun Edwards to be part of the coaching team to face the world champion Springboks.
"I think the Lions is something he would love to get his teeth into," said Robinson.
The Lions are tipped to be coached by Ian McGeechan, who has coached them three times previously and is Edwards's boss at English club Wasps.
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