No you don't need a lawyer unless you anticipate problems or weird RFEs. But be aware that it's not a simple as it first seems, although it's still very easy to do. Just need a lot of form-filling and photocopying of documents. Here's a rough list:
* Cover letter - yes it very helpful if not required, start with a "Dear Sir/Madam" and state the purpose of the application in one sentence (application for adjustment of status based on a pending immigrant petition), and then proceed to list all the documents you have included in the application
* Form I-485 - Application to Register Permanent Residence or to Adjust Status, signed and dated.
* Birth Certificate with certified translation into English.
* Copy of Passport page with nonimmigrant visa, passport data page (main page with your picture), and copy of both sides of I-94 for proof of current status as well as any non-immigrant documents (DS-2019, I-20, whatever)
* Color photographs as per new guidelines (regular US passport photos)
* Fingerprints ( USCIS will notify when and where to provide finger Print)
* Fee : Non refundable Fee: $395 by check or money order (fee may change so check again just before you mail)
* Form G-325A, Biographic Data, all four pages (Adobe Acrobat will automatically fill pages 2-4 if you fill page 1 on the fillable document)
* Employment Letter - on employer's letterhead. This letter should confirm that the job on which the visa petition is based is available to you and it should mention your salary. Good idea to show employment even if its EB-1.
* Copy of your I-797 Notice of Action, showing that your I-140, Immigrant Petition for Alien Worker, has been received
* Form I-693, Medical Examination of Aliens Seeking Adjustment of Status. ( Must be completed by the USCIS authorized physician), so you need to make appointments
* Form G-28 Notice of Entry of Appearance as Attorney or Representative. This will enable your lawyer to represent you (not required if no attorney)
* Form I-765, Application for Employment Authorization or EAD ( Optional, if you want Employment Authorization while the case is pending), include photos and passport page for this as if it is its own separate application
* Form I-131, Application for Travel Document ( Optional, if you want Travel document in case may have to travel out of USA while case is pending), again, assume it is a separate application and include the requirements separately
* You might be required to submit copies of marriage or divorce certificate, death certificate (of spouse), birth certificates for children and certified copies of any arrests or criminal records, depends on your case.
* Other then these may be more documents required and depends on individual case. Some lawyers ask to include 3 years of tax return copies, I-134 affidavit of support (which is actually required for any dependents who apply with you as derivaties).
Good luck.
