Have an efficient layout. Make sure that all the most commonly used areas are close by each other. With the exception of hay storage which should be seperate for fire hazzard reasons, however still easy to access.
Have a system for collection and disposal of manure, even from paddocks. This is helpful in maintaining grass quality and also parasite prevention.
Keep everything clean and in good repair. Have good quality fencing and stay away from barbed wire. Keep pastures clear of junk and undergrowth.
Have each boarder have their own personal tack area/ locker. And have a comfortable (doesnt need to be large) common area with refrigeration, kettle and possably microwave. Also, restrooms and possibly even a shower.
And make the place welcoming for your boarders. Help them to feel at home.
Wash racks with access to warm water, and make sure it drains well so the area doesnt become muddy. Also have a safe area for tacking up that is easy to access from the tack room.
Keep cars and horses seperate whenever possible, and have a dedicated parking area and when planning road ways think about large feed delivery truck or goosenecks,a nd how they will be able to manuvour in the areas you have set.
Plan a sacrifice paddock, to prevent other pastures becoming run down, muddy, weed ridden ect.
There is sooo much more. Any questions, just ask me.