After their Champions League draw at AZ Alkmaar, Clichy has told his team-mates more lapses in concentration at Upton Park on Sunday will prove costly as Arsenal look to continue their four-match winning streak in the Barclays Premier League.
"West Ham are not doing so well and we are, but we have to be careful," said the French defender. "We have to be 100% to get the three points.
"I thought defensively as a unit we played well against AZ. We also had some chances to kill the game, but unfortunately we finished 1-1.
"It is a big disappointment, but we must move on."
Clichy added: "We always want to be the best, but this is a hard competition to win. Barcelona lost at home, Inter Milan were given a hard time at home by Dynamo Kiev. While we do not care about the other teams, it shows how in football anything is possible.
"Away from home, you have to keep focused until the last minute and even with the best players in the world you can lose games sometimes."