The American, who won two Olympic gold medals at his home Games in Atlanta 1996, warns that too much support can interfere with performances.
"People assume there is an advantage with the home Olympics, but there isn't," Johnson told BBC Sport.
"Being too familiar with where you are may relax you a little bit too much."
Johnson said Great Britain's best prospects, such as world champions Mo Farah and Dai Greene, should draw on inspiration from their performances overseas.
"By the time you get to the Olympic Games most of your championships in the past have come in some foreign land, in unfamiliar territory, and you've developed an ability at that point to prepare for a championships in that way.
"The best scenario is to actually try to recreate that sense that you're not at home, so you don't get comfortable and you don't start to get this false sense of security that you might be lulled into with a home Games."
The retired sprinter, who still holds the 400m world record, has predicted that former world champions Jessica Ennis and Philips Idowu should perform well in London, but insists that even the 2011 champions, such as Greene, will not have it easy.Highlights - Ennis wins 2009 World Championship heptathlon gold
"When you look at [Greene's event] the 400m hurdles, it's probably one of the toughest events," Johnson said.
Any one of five or six people could have won that 400m hurdles race [at the 2011 World Championships] and it's going to be the same next year.
He said: "He has an advantage being the champion, but people are still going to be out there training hard and [they will be] ready for him in London.
"Mo Farah is going to have his hands full also with the Ethiopians and the Kenyans. He's had a great year and he's just full of confidence right now but it's going to be tough for them all."