For your reference have a look on the list of reference documents.
Dont neglect to take a single document which leads to 221(g) query. VO is very friendly make sure that you have enough documentation to submit.
Mandatory Documents which supports H1B
iii. Client Letter (If working on client`s location)
iv. Contract with client
v. USCIS Letter
vi. USCIS Letter describing your position
vii. Appointment letter
vii. Employer 2 years tax returns
Documents which supports your profile
i. Updated Resume
ii. Cover letter describes your current roles and responsibilities
iii. Educational Certificates (SSC, Intermediate, Graduation...)
iv. Experience Certificates (Of all years - Offer letters, hike letters, Relieving letters, Experience letters)
v. 1 year pay stubs
vi. 1 year bank statement which supports your pay stubs
vii. Current company and Previous company (2 or 3 references)
Documents which supports your identity
i. Address proof
ii. ID proof
iii. Current company ID card
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