An FIR is not a finding of guilt. It is the registration of information about a cognisable offence, and it sets an investigation in motion. What you do in the first day materially affects how that investigation proceeds.
Obtain a copy of the FIR
You are entitled to a copy. In most States FIRs are also published online, subject to exceptions for sensitive offences. Read the sections invoked, and read the complaint against them — a large number of complaints do not disclose the ingredients of the offence alleged.
Do not approach the complainant
Contacting the complainant or witnesses at this stage is almost always counter-productive. It is frequently characterised later as an attempt to influence witnesses, and it is one of the standard grounds on which bail is opposed.
Preserve the record
Collect and preserve anything contemporaneous — messages, call logs, invoices, travel records, CCTV footage that may be overwritten within days. Evidence that establishes where you were and what was said is far easier to obtain now than months later.
Consider anticipatory bail
Where the offence is non-bailable and arrest is a realistic possibility, an application for anticipatory bail should be considered immediately rather than after arrest. The application is stronger when it is made before the investigation has hardened.
Be careful about statements
You are required to cooperate with the investigation, and you should. You are not required to incriminate yourself; Article 20(3) of the Constitution protects that. Answer what is asked, do not volunteer conclusions, and do not sign a statement you have not read.
This note is general information and not advice on any particular matter.
This note is general information and not legal advice. Please take advice on your own facts before acting on it.
