Question
how can I encourage my dwarf bouganvilla to bloom?

Answer
Do not prune it.  It blooms off of the older growth.  Also make sure it is getting the proper food.  A good balanced fertlizer would do it wonders.  Be sure and follow the directions on the container it comes in.  It may take some time for it to react to all of the above.  Hang in there it could not be mature enough to bloom.  That could be another answer to your question.  With the above care it should thrive for you.

Enjoy
Kristina