There a two basic compass errors that one needs to deal with, variation and deviation. Variation is the error due to the offset of the magnetic pole from the geographic pole and will be on the chart. Deviation is a compass error due to magnetic material in the vicinity of the compass and for a hand held compass should be zero.

There are a couple of aide memoires that help with the conversion from True (the chart) to Compass (what you read on the compass):

"True -> Variation -> Magnetic -> Deviation -> Compass, Add West"
i.e when converting from True to Compass add west variation and deviation, subtract east.

I usually remember it using the aide memoire:
"True Virgins Make Dull Companions, Add Whisky"

The opposite direction can be deduced by simply reversing the above.

Andy