One gross error check I observed that a very experience pilot always made was to write down the ACTUAL ZFW, TOW and LW from the loadsheet adjacent to the figures in the Fuel Plan (of course this assumes that the figures on said plan are about right!).
Recall the crew of a certain airline doing Iraklion to Manchester in A320 did not notice that the ACTUAL load was 5 tonnes more than the planned until they did the first fuel check and were embarrassingly down on fuel to make destination. They had to lob into Luton for some more gas!