The Blues face the League One side on Sunday in the FA Cup fifth round.
"The team has won two games in a row and has to be much better now in terms of how to approach the game with confidence," Benitez told reporters.
"Brentford will try to be compact and counter-attack, and we are favourites and will try to do a professional job.
"From the first minute we have to push and push and try to win."
Chelsea currently sit in third place in the Premier League table.