Plan!
Plan, plan, plan, plan, plan! I cannot stress this enough - taking 15 minutes out of writing time to make a good plan helped me wonders (clearly I am showing my clarity here ;P )
My plans consist of my contention, each topic that the paragraph will be about (not so much topic sentence), and examples - even just "hutu/tutsi rwadna genocide --> consequences of not doing x,y,z". I used to get marked down on clarity and expression and just adding in planning has helped boost my mark tremendously.
In addition to this, picking up a good vocab is key - make sure you know the nuances of each word. Reading helps, but for the cheats way, there's some good sheets scattered about the forum - checking in the sections for Language Analysis is your best bet, as the descriptor words for tone can often be added in for clarity in your context/text response essays.
And just practice, generally, but that's always the answer ;P Good luck!!