Create a hedgerow of bushes like lilac along the perimeter. Place flower beds in hard-to-mow areas. Consider adding a water feature. Keep easy maintence in mind as you design.
I would recommend wildflowers, rock gardens, cacti, ponds or water features or spreading ground covers as landscaping ideas for a yard that is very large and hilly.
With a hilly landscape, the best approach is to sculpt the curves of the ground so as to best accentuate both the approachability and security of your walkway.
