You are not supposed to prepare a return for someone else, unless you are a paid preparer and even then you must enter the necessary information such as your PTIN (Preparer Tax Identification Number).
Print out the tax return, have him sign and date the bottom of the 1040, page 2 and mail it in. Here is an IRS Link with the address you would need to mail the return to, based on state.
He would also need to do the same thing for the state return.