Following standard documents are required to be submitted to Indian Customs for Export Clearance.
Export Valuation Declaration
Purchase Order / Indent / Contract / Proforma Invoice
Letter of Credit
Freight Certificate (If contract is C&F OR CIF Basis)
A.R.E Form.(If cargo is attracting Central Excise Duty)
Catlogue / Drawing / Technical Write up / Litreture
Instruction sheet for preparing Bill of Lading / Airway Bill
Please note that the concerned authorities can call for any additional documents depending on the nature of goods and classification / notification claimed.