Craft a rough draft of the dissertation. You will not be able to forge a perfectly polished draft on your first try, but you will need your thoughts on paper to organize them. Do not worry about spelling, grammar or punctuation on the first draft. Just get all of your information in some configuration so that you are not trying to come up with new ideas during the revision process.
Review the dissertation and smooth out the rough edges of the writing. This will include spell checking, grammar revisions and punctuation. Just cover the basics on the first revision to leave you with a grammatically correct work.
Polish the dissertation one section at a time again, this time being certain to check word usage and citations. This will take a considerable amount of time because of how long a dissertation is expected to be. Do not be afraid to add or subtract information as needed. Review every facts to ensure their legitimacy and relevance to your overall subject.
Give your first revision to a trusted scholarly friend who you know will be honest in his critique. Let him make as many notes as he wants so that you can revisit all of the areas that the editor thinks needs work.
Reread the dissertation once you have made all of the revisions according to the notes that your editor made. Make sure that any alterations do not conflict with the direction of your paper or the research that you had previously done. Read the dissertation out loud to find any passages that might make sense in your head, but are actually jumbled and wordy.
Give the polished paper to another trusted friend or professor to read again. This should be your final revision in the writing process so take every note to heart. Be diligent in your rewrites, ensuring that each one is handled with care.