If playing legitimately, this is by far the hardest achievement in F1 2011. You will have to work on your consistency as a driver to post 5 laps successively that are within 0.25 seconds of each other. For the average driver, this will require a lot of practice and patience as even the slightest mistake will void your run and 0.25 seconds doesn't allow any room for screw-ups.
Here are some tips to help you practice for consistent lap times:
Use the Red Bull. It is the smoothest car to drive and has the best traction.
Know your braking points and stick to them. Try to find markers around the track that make it easier to set up a braking point you can remember.
Stick with your shifting-rhythm, meaning: try to downshift on each corner like you did in the previous lap.
Use KERS and DRS on the same parts of the track on each lap.
Don't force it. If you're not having any luck, stop your session and unwind a little - trying to force it usually makes your lap times worse.
Luckily, you are allowed any and all driver assists.
Alternate method (easier): See this post here.