One of the ways to handle the increasing demands on readers' skills is to make writing more readable. The problem has two different aspects: predicting how readable writing will be to a reader, and producing writing that is readable to that reader. Prediction is relatively simple, and can be done statistically with readability formulas. Production is more complex, and involves changing words and sentences that can cause difficulty. This manual covers both aspects of the problem, with emphasis on suggestions for changes that can make writing that is designed to inform or instruct more readable. The chapters are organized in terms of a simple model in which the reader's performance is affected by the interaction of level of competence, level of motivation, and readability of writing. The suggestions made in this manual are, insofar as possible, based on recent research in psycholinguistics and readability. (Author/DDO)