I have to admit that stage plays aren't really my specialty. What I do know about them is that the formatting is much more relaxed than screenwriting and there are very few set-in-stone rules that must be adhered to. Playwriting is mostly about coming up with a format that works and is clear for your reader. (We'll get into screenplay format in a week or two.)

I did find this link that might be helpful: http://nycp.blogspot.com/p/playscript-formatting-template.html

It has both a list of stylistic requirements by the Yale University Press, as well as a MS Word template you can download to guide you.

Hope this helps! Let us know how it goes!