The French label for sustainable stables Equures has some tips for that.
You can find more info here:
In Germany they promote biodiversity at equestrian locations. More about that here: http://thesustainablehorse.com/germany-promotes-biodiversity-equestrian-centers/
Try to firstly record your current situation. How much energy you use, how much gas/oil you use for heating? What kind of chemicals? How is your mineral supply organised, what happens to the manure? Make a plan from there.