I’d go to the AICPA mock exam for BEC and review the sample responses for the writing sections. They show you the exact ideal layout in detail. Grammar and structure are very important, so I’d focus on those areas heavily since you are a foreigner. Ultimately, if you score highly on the MCQs and SIMs and have decent responses for each of the writing sections you’ll still be able to pass since it’s only 15% of the exam. Good luck!