Start With Form 16, Everything Else Follows From It
Form 16 is the one document your employer is legally required to give you by June 15 each year, and it does most of the heavy lifting for a salaried ITR. Part A of Form 16 shows the TDS your employer deducted and deposited with the government. Part B breaks down your salary, allowances, and the deductions your employer already accounted for under Section 80C. Before you open the Income Tax e-filing portal, download Form 16 and cross-check it against your Annual Information Statement (AIS), available under the "e-File" tab on incometax.gov.in. If the TDS figures don't match, the mismatch will flag in processing and slow your refund. Catch it before you file, not after.
