Pick a style guide and stick to it--reference books like Words into Type, The Chicago Manual of Style, etc. Refer to it for stuff like series commas, capitalizations, abbreviations. Consistency is what you are after and you might as well start at the beginning of the process.
I also highly recommend keeping a list (handwritten or spreadsheet) of words you use over and over which may have different variations--names, cities, companies--then you can refer to it so that it is always used consistently. Confirm spellings of names at the start, refer to your list, and make sure to double-check yourself. I was just reading an essay and a recurring name was mispelled right in the middle of the piece--readers notice stuff like that, and you shouldn't rely on an editor/proofreader to catch everything.
I just take a pad of paper and put a letter at the top of each page, all “A” words and names get written on the “A” page. It's not fancy but it works.