Integrating permaculture into an existing garden

I've been offered a chance of taking care of a garden that has been abandoned for a couple years. I have little hands-on experience with permaculture (or gardening in general) and I haven't been there yet, so right now my priority is to learn how to observe garden ecosystems, so that when I soon visit this place I can make any meaningful conclusions. The plot is in a rural area in central europe, next to a forest. We are in early stages of discussion with the owners so I don't know much, but there are nut and fruit trees and I can expect the entire place to be a bit overgrown.

I already started reading Gaia's Garden, but what resources would you recommend to have any idea where to start and what to look for?