well, its the old rule of 'everything in moderation' (this applies to eating too!) and repetition - if you don't enforce what u have learnt in class that day u will forget it. even though the prelim. course doesn't count towards your final hsc mark: save the excessive stressing and worry over your marks for next year (or term 4, i should say)- theres heaps of it!, you can get yourself into routine and learn to study, so you dont fret over it when the hsc looms from behind. i did studied harder than most - some pplz excuse was "its only the prelim" i came first in biology, legal studies and geography, 3rd in chemistry (i'm coming 2nd now!) etc. but remember don't stress too much over the prelim!