http://www.ukba.homeoffice.gov.uk/britishcitizenship/applying/applicationtypes/naturalisation/The biggest thing for you is that since you got ILR so long ago, you will have to take the Life in the UK test. There are lots of threads about how to study for it and how to take it.
The form is form AN, and it's really very straightforward. You'll need two references who have known you for at least three years, at least one a British citizen and one a professional.
I'd recommend using the Nationality Checking Service, that way you can keep your passport while your application is being decided, and you'll get feedback on your application.
Finally, make sure that when you apply you were physically in the UK three years before. It doesn't matter how many years total you've lived here, the requirement is that you were physically present exactly three years before on the day your app is opened.
