In order to effectively desciribe you should -
Play on the senses, describe not only what the character see's but what they smell, hear, touch and taste.
DON'T BE BREIF! The aim is too describe so instead of just saying 'He opened the doors' add detail! 'His sweaty hands pushed against the cold glass and he took a deep breath. He pushed the wide door open, and without time to consider running, he was inside.'
Use linguistic techniques, you have been learning about them so actually use them now! Similes, metaphors, colluquialisms, visula imagery, syntax, onomatopoeia. ALL OF THEM will gain marks! Using an extended metaphor is sure to guarentee an A.
BE imaginative. Even if the question is dull you can do anything with it! 'Describe a journey by car' could be a kidnapping. They give you a lot of scope to make the answer interesting - you want to INTEREST the examiner.
PRACTICE. Right now, describe the room you are sat in, use all of the techniques above. I know its cliche but 'practice makes perfect!'
Okay, arguing is easy, we all do it - we just need to put that into writing.
Firstly, the structure of the argument should ALWAYS be - Your argument, the opposing view, and then countering that view and basically owning them ;) Just write pasionately and over exaggerating never hurt anyone.
Statistics - make them up! Obviously not unrealistic ones like '97% of people have fallen down a well'... because thats just stupid. But try and sound intelligent
Use fact and opinion. Make a clever point then explain how and why this backs up your argument.
Anecdotes can work in an argument (if in context) don't just whack out some story about your nan because suprisingly, it won't get you marks...
Humour can work effectively in an argument, to knock down the opposition you can use sarcasm and irony.
Rule of 3 is always good for getting your point across. It's simple, easy and effective.