"What is the best way to set up graphene to become as invisible to ad tech as possible?"
As stated before, the best approach is to use privacy friendly apps and only those you need.
Aside of that you can still block trackers in DNS level.
You can use a VPN with ad/tracking blocking capabilities.
Or you can set up a private DNS under settings.
Or use an app like nextguard (will take the VPN slot)
Remember that every Information you willingly give to an application will still be used to build a profile.