My advice would be to start small and progress in easy steps. Get a small bit of garden going. Weed it, fertilize it, and get something growing. Aim to get a new bed going every 2 weeks or a month. In no time you'll have a great garden.- Dale
I moved into a yard that was so overgrown with trees, bushes,etc. Loads of rubbish to remove. I started with making a walkway and burning all rubbish. Then for the garden, I started at the front edge and worked back.
I got a great tip for me from YouTube, and that was to have in a bag at the back and front door some clippers, gloves, etc. So that each time I walked out I could cut or prune a little off and slowly get rid of that. Now I am making an ad hoc, hotch potch area in front garden and reducing the grass area so I don't have to mow.
I would suggest you get a pencil and paper and draw out how you want the garden to look in the end. No matter how bad your drawing skills a simple floor plan is all you would need. Mark out where you want proposed things in the future - garden beds, tool shed, chicken coup, grassed area, shrubs, etc.
In some areas you could spray poison, especially with tall grass and weeds. Then work each small area at a time, once you complete one section go on to the next. It is amazing how your confidence and enthusiasm will grow after having finished one small area! - Wayne