If the validity of a report has to be defended in court, a judge or jury who sees typos may conclude that the report is substantively unreliable. Frankly, this is an illogical conclusion but I have heard the claimant's attorneys make this very argument. It is difficult to proofread your own reports. If possible, have another person read the report for typos. If time permits, set the report aside for a day and read it later.
Fresh eyes detect errors far better.
Recalculate all the math. I repeatedly see arithmetic errors in my cases. Attending seminars by trade organizations, reading industry publications and networking with professional colleagues will keep you abreast of industry developments. If a client asks you to include or exclude anything unusual from your report, keep notes of the request. After a conflict develops, clients frequently tell me that the claimant requested that the disputed material be omitted from the report.