Verys easy, you dont need an attorney for this. Read the instructions carfeully in the forms and make a check list of all the doc required, they have mentioned that very clearly in application instructions. Fill the form and submit.
I never put a cover letter with any applictions I had maile dot USCIS, no use, I wonder the contractors whoc process your applicatiosn ever read that.
Instead I always use filing sheet protectors (thos clear vinyl sheet protectors you get in staples or office depot or office max or walmart) and staple and consolidate all documents pertaining to one application in each (this includes, check, photographs, supporting docs etc). This is particularly important when you are filing multiple applications and sending all of them in single package. Other than this I laser print and paste the checklist of all the documents and applications contained in each sheet protector, so that thye come to know that what all I have attached with each application.
Good luck !