ATPL F/P exam
I self studied and passed comfortably, so I'd say the key is a comprehensive set of notes with lots of practice questions + lots and lots of practice. (I also had the aviation theory centre flight planning book, which was a good read but there is no pratice material in it).
Start slow, build up the accuracy and develop a method for each type of question working slowly. Dont try to do an exam in the time limit available at first, you'll just be disappointed! Whenever i didnt get the answer in the notes, i worked back to find the exact point where i went wrong and re-worked the answer. (more practice). This assumes that the notes you are using have the full worked flight plan available.
Then gradually work up the speed.
I think with the F/P exam theere is more than enough time if you work steadily and accurately. Its when you make an error that you have to rework a significant part of the plan, or if you have to stop and ponder how to go about the answer - thats when you'll run out of time. I had 23 min up my sleeve at the end.
My 2c.
edit: the sequence of calculations that you need to perform is important for most questions. Get a feel for the best order to crunch the numbers. If you have to drop one line of thought to go do other calcs, its a loss of continuity and a great chance for errors to creep in.