The basic advice we are given is that if you read it on a plate or a chart you need to correct it and if you are told it by ATC then it will have already been corrected or the min. altitudes normally used will have taken into account the worst case. Have to say I don't really trust some of places we go to have done it so keep an even more careful eye on terrain and clearances if the temp is really low. Some of the corrections required to approach fixes, base turns and high MDAs can be pretty large if the surface temp is way below ISA, watch out.