Writing is a skill. It can be developed by practice and active reflection on your strengths and weaknesses in your writing. Where possible, let a colleague read your report and ask for constructive feedback. The Report Checklist may be useful here. Approach someone who you feel is experienced and from whom you can accept feedback. In addition, you should also look at other reports to notice what writers have done well and to consider how you could apply similar structures and conventions to your reports.
Once you are aware of where you need to improve your written communication skills, decide how you will go about improving your writing.