Hi Francis,
You have to wait for 12 months after you have been granted ILR. As taken from the
UKBA guidance, "You must be free from immigration time restrictions when you apply for naturalisation. Unless you are married to or the civil partner of a British citizen, you should have been free from immigration time restrictions during the last 12 months of the residential qualifying period."
Which form you use depends on the kind of application you are making. The majority of applications are made using Form AN, but if you are making an application with any extra considerations - for children for instance, or if you are applying as a British Overseas Territories Citizen - then the form is different. Some summary information and links to the appropriate page on the UKBA site can be found
here.
Finally, the official line on waiting times is
six months, but people may have different experiences from their own applications.
I hope this helps
George