i've completed my preclinical medicine and intercalated bsc and gained a first. basically i found that you really need to know the basic, core textbook stuff and also be reading around stuff that the lectures don't mention, and also the up-to-date ground breaking stuff. the year just gone (intercalated bsc year) i read about 10 papers for only half the modules, and there were 10 modules. if only i knew about the importance of paper reading and wasn't so lazy at the beginning, i would have got a much better mark.
the intercalated bsc part of my course had essay based exams, and you really need to show you know the basics back to front and then impress them with something different, not mentioned in the lectures and with up to date research or examples.
the other parts of my preclinicals were mcq and emq based, and you still need to know every single point in the lecture and know everything back to front, and beyond if you want to get top 10-20% at my uni. there were names and diseases in the exams that i had never heard of in the lectures at all. the only way you would have come across them would be from your wider reading. which is very tough to ask for given the sheer volume of 'basic' stuff we are meant to know.
edit: also regarding essays, you need to learn not to waffle and just write down everything you know around a subject because you are panicking or you don't know enough to answer the question. this is another thing i learnt, which was my tactic the last time i had essays to write, probably GCSEs and got very good marks doing that. however at degree level, it just doesn't cut it. it is very obvious when you read the essay.
another point i should mention is that different unis have different expectations of what is first/2:1 etc material and where the boundaries lie. i guess you just do your best at the beginning and suss out if your work and effort is at the level you are satisfied with. if not, ask advice from your tutors, lectures and past students.
good luck guys.