Boss wants more balls put into the box.
The U's go to Griffin Park looking to bounce back against the Bees, following a heavy defeat at Tranmere seven days ago.
And John is keen for his players to get more crosses and balls into the box this weekend.
"We haven't created as many chances or put as many cross into the box as we would have wanted to.
"Those are big parts of the game and I think that we have the the firepower in the team to resolve that on Saturday."
The Bees have had a solid start to the season, having only lost one of their first four matches. However, that defeat came at Griffin Park, offering the U's hope of getting a positive result this weekend.
"The lads have been frustrated with the result last Saturday, but we spoke about it on Monday and have been positive since then.
"We have been reasonable so far this season, but I think that 45 minutes at Tranmere aside, the performances have been decent.
"We will look at how Brentford play but also approach the game positively ourselves this weekend."
The game will be live on U's Player this weekend. To get involved, click HERE to find out more details.