Do you actually want people to read and understand your reports?

The first duty of any publication is to be read. Since people read documents for themselves, not to please the author, you had better work hard at winning their interest.

Content - keep it simple

No document should contain more information than it needs to do its job. Where you need to include technical detail to back up your conclusions, run it separately from the main text.
     Brevity isn't just the soul of wit, it is a golden rule of all communication. Begin a long report with a 1 - 2 page summary so people who don't have time to read the full report (that's most of us) won't have to.

The title - tell them what they're getting

Your title should 'sell' the document to the reader while announcing clearly what it is - double titles are particularly useful, eg:

RUNNING WITH THE FOX
A study of the impact of the hunting ban on rural communities

Style and language - don't show off

Avoid unnecessary technical terms, however clever you think your readers are. Even highly-qualified professionals understand plain English best.  Gratuitous jargon will immediately brand you in most people’s eyes as a know-all who can’t resist showing off your membership of an arcane professional group.
     Long words (by which I mean those with lots of letters) are not necessarily wrong – it isn’t the brevity of a word that matters so much as its value and familiarity. ‘Neonate’ is shorter than ‘new-born baby’, but I know which I prefer.
     Do check every adjective and adverb to make sure you need it.

“When you catch an adjective, kill it”
- Mark Twain

If you don't find it easy to write fluently, a useful approach is to write as you would speak, then sort out the grammar and syntax afterwards.
     If good writing doesn't come naturally (or you simply don't have time), ask a professional copywriter to help. You can save on their time and your budget by preparing the document in your own words, then handing it over for redrafting. With email this is very easy. Email Chris Newton Communications for help.

What is a sentence? 

A sentence must contain a verb, otherwise it's just a 'fragment' - a useful rule, in the same sense as not crossing your hands on the steering wheel is a useful rule, particularly when you’re learning to drive.  But fragments are used widely and freely in popular writing, not least because human speech is not composed entirely (or even mainly) of sentences.  So I'd suggest that it's one of those rules it's perfectly ok to break as long as you know you're doing it, and why.

Clear writers, like clear fountains, do not
seem so deep as they are; the turbid look the most profound - Walter Savage Landor

What paragraphs are for

Some people assume paragraphs are BSI units of length, others just want them to look nice on the page. Graphic designers often bend over backwards to end a paragraph neatly at the foot of a column. But the real purpose of a paragraph is to deal with a particular subject or area of the subject. When you read from one paragraph to the next in well-written copy, you should always have a sense of a natural pause between two connected topics or points. Likewise you should not find yourself tripping over a change of theme in mid-paragraph.
     If your paragraphs are very long, you may be going into too much detail.  If they seem too short, you are probably on the right track. A paragraph can perfectly well consist of a single sentence.
     Or even less.

Signposting helps the reader

Include plenty of simple descriptive headings to help the reader to find what he wants quickly and easily. Use boxes and hatched panels to help the reader identify specific classes of information, such as technical references or questions and answers.
     Formal reports and technical documents may need paragraph numbering. For the rest, use headings, subheadings and bullet points to break up the text

Limit your type area

Don't crowd the page. It looks daunting to read and can cause duplication problems. The type area on an A4 page should be no more than about 250mm x 170mm (which may need to be offset to allow for binding).

Justification or 'ragged right'?

Type can be set 'ragged right' (as here) or justified both sides.  Many people like the neatness and order of justified text, but ragged right copy has been proven to be easier to read.  

When designing for IMPACT gets in the way

You know those ads which try to hit you between the eyes by setting different words or phrases in contrasting fonts, weights and colours?  Some designers obviously think this looks great.  In fact it makes the text harder to read and the information in it harder to absorb.  It's the written equivalent of changing your vocal pitch and accent every few words when giving a business presentation - ridiculous!  Getting information across in text is all about helping the reader.

Typefaces and sizes 

Normally only one typeface should be used for the main text of a document, with perhaps its bold variant or italics to distinguish key passages and a second typeface for a different class of material, such as technical footnotes or captions.  If you use several typefaces and sizes you will simply distract the reader from what you are saying.  You wouldn’t keep changing accents while giving a speech, so why do it with written copy?
     The lower limit for easy reading of body copy is about 9 point, but on A4 documents 10 point is as small as you need to go.  Excessively large type can be as irritating to read as small type, because the eyes have to move faster to keep the brain 'fed'.

     The role of illustrations

Clear illustrations are a tremendous aid to comprehension, but please keep them simple, caption them properly, and don't inflict big and complex graphics files on users with less computer or printer power - or less time - than you have.