Tips....

ALWAYS write something with which u are comfortable in a debate
Dont choose a topic just cos u think u can write 20 pages of boring stuff in it!!!

if ur able enough, try to opt for something thats a bit different but which u know something about...

THINK and PLAN out ur essay before you write, otherwise it doesNOT read though well.. infact, it should read through like an expert ice-skaters routine (as if ur water flowing through a stream).. no break ups, no ill placed thoughts, it HAS to be coherent and read as if one thought naturally gives birth to another... that is IMPERATIVE.. so i'd suggest rather than just scribble to save time, plan it out, that saves time in the end!

DONT WORRY.. relax.. its all a matter of nerves, and how well you can assimilate stuff u've been studying since u were in the 5th grade!
Its really the depth in your thoughts, how choherent they are, how well you place stuff, how thought flows from thought, and how well it reads through.