The Reds were slow out of the blocks in the opening 45 minutes of their Capital One Cup first round tie at The Highbury Stadium.
But they improved significantly after the break once O’Driscoll had pushed Greg Halford into a holding midfield role and asked Andy Reid and Radoslaw Majewski to operate in wider positions.
Dexter Blackstock’s 57th minute goal killed off the challenge of League Two newcomers Fleetwood and earned Forest a place in the second round of the competition.
O’Driscoll said: “Sometimes at half-time you have to take chances but it was a logical decision to make.
“The players responded to it which is a plus for me. We told them what we wanted them to do and they understood it and by and large it worked, so I’m pleased with that.”
O’Driscoll will now step up his plans for Saturday’s Championship curtain raiser against Bristol City at The City Ground.