How they learn, play etc. Whether you need to provide food or whether they do, do they accept funding, is it term time too, where they sleep for nap time, flexibility with holidays, sickness etc, recommendations from other parents in the area, look at their reviews, ofsted rating
It’s pretty personal but I’d say look at their staff to child ratios and set up; depending on your preferences you might want to ask about learning / engagement styles and how they encourage this I.e outdoor play etc; flexibility around holidays and if you needed to change a day; what they require you to provide; policies around the free hours (I have zero clue about this myself!) and, of course, cost! If you’ve got a local neighbourhood FB group it might be worth asking in there for word of mouth recommendations too x