The simplest way is to use make dynamic search selections like:
=Month=month(today(2))
and save the document in that state. However, most of us mess this up by saving the document in a cleared state. You can save your selections in a bookmark and remember to apply the bookmark before saving, However, I usually mess that one up also.
See this blog post
http://qlikviewnotes.blogspot.com/2010/02/setting-initial-selections-in-version-9.html
for an explanation and examples of setting initial selections on open. My current favored method is to save intitial selection state in a bookmark and apply the bookmark in an OnOpen action. Strictly speaking, OnOpen is documented as being unsupported in the server environment. However, I have yet to encounter a problem using to apply a bookmark.
-Rob
