Is there any really good guides on how to be gdpr compliant as an engineer?

I want to know what I need to implement in my software so that should I need to respond to a gdpr request, I can action it as required. Someone else can deal with third party notifications etc, but I want to know how to create a ‘nuke this user’ function, but I don’t even know what data a user can supply for identifying purposes (their name? email address? IP?) nor what data I must destroy (name? email? Ip?)