Sour Cherry Tree dropped leaves early- how to keep alive for next year?

So I have a sour cherry tree in my backyard. It dropped its leaves early this year, I'm not sure why. I think it may have been water related. There are still leaves on the tree but probably more than 90% have already fallen. I have gathered the fallen leaves and removed them from the area in case it is Cherry leaf spot. What should I do now and over the winter and early spring to make sure that it comes back alive next year and gives me cherries?