Most questions in Q1 section of the paper and others can be checked so that you can be absolutely sure you have the correct answer. Any rearraging, simplifying, factorising etc. questions I always just substitute in a value for the pronumeral, and check that both sides remain equal, or with rearranging that the given expression equals your answer when values are substituted.
Other questions I redo in pencil in the margins (don't rub out though, you may have the right answer in the margins) or if I don't have time to completely redo I check each step in my working, making sure I haven't done anything stupid.