Good legal writing requires short paragraphs made up of short sentences.
To shorten sentences, delete extraneous words. But don’t delete all descriptive words such that your brief becomes a dry, choppy document devoid of feeling or persuasive effect.
Another way to shorten sentences is to ask yourself if that comma in the middle of that long sentence can be replaced with a period. Usually it can and the reader will benefit from not having to wade through and re-read a run-on sentence to understand the multiple points contained therein.
To shorten paragraphs, make sure you have a good topic sentence and that all following sentences stay within that topic. If more than one topic is discussed in the paragraph break it down into separate paragraphs. When you do so, however, remember to make sure there is a good transition sentence at the end of the paragraph in order to create a good flow through all of the paragraphs that builds like a crescendo towards the desired result.
Another good form to utilize persuasive headings and sub-headings to guide the reader through your brief to the desired destination, i.e., the acceptance of your position.