I think one thing which really helps is to be very vigorous about your notation and presentation of working; I found this tends to minimise silly mistakes. Don't just write down "n = 20/32" when finding the amount of oxygen in 20.0g of molecular oxygen, write down:
n(O2) = m(O2)/M(O2) = 20g/32.0g/mol = 0.625mol
Additionally, note the inclusion of units during all stages of working; you'll know you've made a really silly arithmetic error if your units don't work out!
Other than that, make sure to make a list of mistakes you commonly make (e.g., I always used to lazily put M(H2) = 1g/mol instead of 2g/mol), and even if you don't have time to drill it into you to not make the mistakes to begin with, if you have time at the end and know what your common mistakes are, it will make your 'checking over' tie a lot more efficient.
highlighters. these bad boys are SO important.
Use a different colour for different parts of info. For example you might use one colour to highlight all info for a particular substance (mol, conc, titre) and then another colour for dilution and maybe another for the units you have to put it in. Not only does it make things easier for you to track info but its also a huge time saver... well for me it is.
Be careful about this - don't highlight anything on your actual written answers; when the papers are scanned, anything highlighted just turns black! Don't highlight your final answer to make it stand out or anything! Haha.