The most common mistakes here are to do with carries.

Here is a list of dos and dont's that should help:

•  always write the carry - you will forget it!

•  place it below the answer line - easy to ignore it anywhere else

•  put it in the correct column - it must have a real value

•  don't cross it out as you use it - easy to cross out but not add on

Here is a set of wrong answers showing each of the above:



And the right answer!