Students often tell me that they are stuck on the same writing score. For example, they keep getting 6.5 in every test they take. If you are stuck in a rut like this, perhaps the most effective way to get out of it is to give more importance to your essay plan.
I tell my students to spend around 3 minutes making notes for each main body paragraph. So, for the housing topic we've been looking at recently, we would spend 3 minutes thinking about why we shouldn't build more houses in cities, and 3 more minutes thinking about the benefits of developing new towns.
The act of planning helps you to separate the task of idea generation from the task of writing. It's extremely difficult to do both of these things at the same time.