First make sure the rotating section is properly centred and all the screws on the CRP are done up tight, not doing this it is easy to end up with big errors and the biggest cause of wrong answers.
Hopefully I do not need to explain how to do it, but just in case - heading at the top and TAS under the centre circle - use a SHARP pencil and draw a line on the drift and another round the Groundspeed. Rotate until the cross so formed is immediately below the centre - read off wind direction at the top and speed as the difference between the centre and the cross.