When writing reports, you might find useful resources at the following sites:
Style Guides
A style guide gives advice on all aspects of writing, but especially on use of language, punctuation and layout. If you have a writing-related question you might find the answer in a style guide.
I would recommend The European Commission's English Style Guide. This is a superb resource for writers in international organisations. Updated May 2008, available as pdf file. This style guide came out of the European Commission's 'Fight the Fog' campaign for clear writing.
For other online style guides in both British and American English see my review here.
Report Writing
For additional tips on report writing you might find this site from Surrey University (UK) useful. Bear in mind that a lot of internet resources on report writing are aimed at university students and apply mostly to reports in the sciences. This site also addresses report writing at work.
The Online Writing Lab (OWL) at Purdue University (USA) has good material on professional writing in general as well as advice on memos, reports and letters. Useful and easy to read. The home page links to resources on punctuation, grammar and spelling. This is probably the biggest and longest running OWL on the web.
Access to United Nations documents such as resolutions, missions reports and official letters has been made much easier by the introduction of the UN Documentation Centre. You can learn a lot about the conventions for UN reports and correspondence by simply browsing this site.
It is also worth looking at the way reports are written in large NGOs. See, for example, the reports in the Amnesty International Online Documentation Archive and Human Rights Watch Publications. Human Rights Watch reports are particularly interesting for the way they are structured and the use of headings/sub-headings.
Writing and Editing
The Plain English Campaign is a UK group promoting the use of clear written English in government, law and business. Go to 'Free Guides' for PDF versions of their useful and practical writing booklets, including 'How to Write Plain English'.
If you are a legal professional (and even if you are not!) you may find Bryan Garner's Legal Writing in Plain English useful. This is the free online version of his book, but there are many tips on how to edit your (legal) writing to make it more reader-friendly. Also includes exercises.
For my tips on editing see here.
For more resources on writing including a review of online dictionaries see here.
