As a general rule for plain or simple fruit scones you would use 25% butter to flour. So, for 2 cups (10 oz) flour you would use 2.5 oz (5 TBS) butter.
Use cream instead of milk - about a cup for the same 10 oz flour.
You can add an egg to the mix for a scone with a slightly cakey texture and while scones are best the same day, adding an egg lets them keep a bit longer. If you do add the egg, reduce the cream to 3/4 cup and the butter to 4 TBS.
One other thing - don't roll or pat the scone dough to less than 3/4" thick otherwise they won't rise properly. Don't know why, they just won't.