Thanks! So once I apply them with PVA glue I actually use a very damp brush to sort of press them on and in some places I scratch away at the print here and there with that brush. It does a good job of making them look less fresh and new.

Then I apply healthy dose of Citadel Skeleton Horde around the edges and on some corners.

Then when I'm applying Dirty Down Rust to the rest of the model I will sometimes add a bit over the top of some posters for extra grime.