Section 154 CrPC
All information that the police receives relating to offences that are cognizable (that is those for which a police may arrest without a warrant) given orally or otherwise to an officer-in-charge of a police station shall be recorded in writing by him or under the his direction and must be read over to the informant and signed by him. This FIR must be entered in the Station Diary or any other official record book of the police station.

If the police refuse to record an FIR, any person may send in writing, by post to the Superintendant of police;

An FIR cannot be filed on the basis of rumor;

An FIR is not substantive evidence;

It is a document on the basis of which investigation is commenced;

Where the original FIR has been suppressed and in it's place another document supplemented it loses validity;

Where the FIR is lodged after a delay of three days and the conviction rests mainly on the uncorroborated testimony of the injured, and there was past enmity between the parties, it has been held that the charge in the FIR was not proved beyond reasonable doubt;

In case of serious offences like death by poisoning or throttling, a few hours delay is justified.