I hate design a prac questions, I always come up with the most ridiculous experiments, but somehow get fairly good marks for them.. It's weird!!
I think the best way to do well in those questions is to know the features of a good experiment- all the stuff like its validity and reliability, measurability, availability of resources, being carried out over a practical amount of time, all the variables being defined and controlled, blah blah blah.
My bio notes are so long, around 20-25 pages for each topic, excluding pracs, It's crazy!
I haven't even started my other subjects yet :S