A good yard who knows what they are doing should quarintine for 2-3 weeks when horses move on and worm so ask about their policy.
What there worming programme is? and do they take samples?
Lorry parking
Can you have individual or small group turnout
If you can choose turnout times as in either leaving out 24/7 in summer or turning out at night in during the day. What is the grazing like in winter - do they go out in morning and come in at tea time.
Lorry/trailer parking
Arena rules - are there certain times you can book the schools for lessons etc, can it not be booked at busy times.
Quality of hay/hayledge - do you buy it from the yard, or do you buy it from some one else and they deliver it to the yard or is it in with livery price. How much are you allowed or is it ad lib?
Security - is the yard and tack rooms always locked unless someone is there?
Shavings do you buy from them, in with livery, buy form someone else but they deliver it.
How much space do you get to keep your feed, shavings and hay/hayledge in?
What is the poo picking rota? do they get a weelbarrow full out a day of do a lot once a week. I'd mae sure the paddocks are clean from muck shows a good yard, and low worm count. Paddocks free from weeds and toxic plants like ragqort.
Definatly look for good fencing - certainly no barbed wire, preferably not wire, good post and rail or elecric fencing.
Horses looking happy and helpfull is always a good sign. Hay/hayledge stored properly etc.