Mail all forms and schedules, do not mail worksheets. Include a copy of all tax documents that show any federal withholding. Use the same information for your state return if applicable.
Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS or state received the return.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.