"It will be a very passionate atmosphere and people are going to let you know what they think of you," said Johnson.
"It can be really noisy around the back of the dugout and it can make you a bit paranoid.
"It's hard being in an away dugout these days - if you've got the wrong shoes on, or you're bald, or short, then you've got thousands of people quick to tell you so. You very quickly get a complex.
"All managers can lose it, but I'll be trying hard not to.
"And it's even more important for the players to behave and control their emotions.
"They have to have emotional control, they have to be aggressive without being angry and they have to let their heads rule their hearts."
Johnson revealed just how much today's game means to him, his side and the Bristol City supporters.
"This is our local derby in the Championship and, as such, it always means that little bit more," he added.
"It also means we have to be extra careful not to overstep the mark and lose our discipline.
"You battle for everything within the rules of the game, but you cannot afford to cross that line.
"If any of your players go beyond that line, it can cause you problems.
"If you're not professional, then the three points is much harder to get.
"We have to play hard and play to win, but we also have to make sure we stay within the laws of the game."
With Johnson determined to continue his side's unbeaten start, he continued: "They do make a roar at Cardiff and it is an intimidating atmosphere. But we can use that to our advantage.
"It can help create a siege mentality and that's something we've already talked about earlier in the week.
"We've proved we can win football matches away from home in the Championship and we're going there to get a result - despite the atmosphere.
"Dave Jones will be telling his players to use the crowd in their favour and we have to try and turn it around and make it work for us."