How do I score high marks in writing tasks?

Generally, in writing tasks you'll mainly be assessed on the accuracy of your grammar and how complex your language is without leaving out information. It is important to know basic grammar (i.e. verb conversions) for simple sentences. It is also usefull to make sure you know some more complex sentence structures that you can easily put relevant information into (e.g. "In tegenstelling tot... geloof ik dat....')