First form that is overlooked a lot is the Certificate of Compliance. This form is signed by the applicant and just promises the ATF that the applicant is a US citizen. Only 1 copy is required with application. Filling out is self-explaintory with the template.
Going the Trust route makes the process go a little easier as no fingerprints, photographs and CLEO signoff are required. The Form 4 should be very easy in that a majority of the NFA dealers charge a premium to transfer NFA items and part of the service should be to complete the form for the customer as the applicant should only have to give the dealer their basic information as most of the form has to do with the dealer and the item that is in the dealer's possession. This is here just to make sure that everything is filled out correctly before submitting as even dealers make small mistakes...enough to kick back an application which can add another 30 days or so to the approval process.
On the back all the applicant needs to do is check the boxes and sign their name, "trustee/settlor" (however they are called in the Trust) and submit the application in duplicate (the forms MUST be printed front to back as the ATF won't accept any applications where page 1 & 2 are on seperate pieces of paper) along with a COPY of the Trust (it won't be returned to the applicant) along with a copy of Schedule A (Trust assets) and Schedule B (beneficaries). If the Trust isn't submitted, the application will get kicked back.