Here is all what a common man can do if police does not register FIR.

a) Talk to SHO of the concerned Police station and ask him to register FIR. Most probably he will try to persuade you not to register FIR and instead ask you to write complaint on a piece of paper. Police is bound to take action on FIR as they need to give explanation of each & every FIR registered in a month to the district magistrate. No such boundation exists for a complaint.

b) In case SHO does not register your FIR (which will be the usual case), you can meet ACP or DCP of that zone.

c) In case you can't take off from your office work, write a registered mail to DCP with a copy to ACP or district magistrate of that district with a copy of the complaint and asking for an explanation that why your FIR was not registered?

d) There is a website of delhi police where you will find all the relevant persons of all dcps, acps and commissioner of delhi police to whom you can contact through email.

e) If nothing works out the last thing you can do is to call up at this number and register your complaint on phone itself.
For Police related complaints you can also contact to Flying Squad of Vigilance Branch : (011) 23213355.

Refer these websites for further information:

http://www.delhipolice.nic.in/home/contactus.aspx
http://india.gov.in/outerwin.php?id=http://mha.gov.in/
http://pgportal.gov.in/

http://164.100.42.72/rti-mis/

Getting your FIR lodged is absolutely must as it makes police accountable to take action. This will definitely help to bring down the crime rate.

f) If Police does not take action on your complaint or FIR you can file a 10 rs RTI which is a handwritten application to be deposited at DCP of that zone.