Biometric enrolment for ILR visa!

Hello

Do I wait until the application is being processed for them to tell me to enrol my biometric information or am I supposed to do this before I send my visa application?

I have read of people doing both. I am coming of my Ancestral visa so maybe that makes a difference?

Thank you

HO will write to you to go an enrol biometrics. The letter must be taken with you to the Post Office as it has a barcode on.