Mistakes: we all make them. When it's in the context of filing forms with the US Patent & Trademark Office, those mistakes may result in additional fees. They can also put intellectual property rights in jeopardy.
To help inventors avoid mistakes, the USPTO offers several places to go for help. Two, which are accessible at any time, are Common Pitfalls on USPTO Forms and the March Inventors Info Chat, which had the topic Common Mistakes and Support After Filing.
There are also places for in-person, phone, or email assistance: the Patents Ombudsman Program helps when applications get stuck during examination, the Pro Se Assistance Program helps inventors who are filing a patent application without an agent or attorney, and there are pro bono programs for both patents and trademarks across the country.
And don't forget your local Patent & Trademark Resource Center, located in the Central Library of the St. Louis Public Library!