The book referenced above by St. Alphonsus is wonderful, and I also highly recommend "Holy Abandonment" by Rev. Dom Vitalis Lehodey, O.C.R. (written before Vatican II and goes into great detail about how to find God's Signified Will and His Will of Good Pleasure in your life, discusses ways in which God manifests His Will for you, how to deal with inspirations, using prudence in discernment, etc. A real gem of a book). I consider this a MUST HAVE for a spiritual reading library.
Another good one is "The Holy Will of God: Source of Peace and Happiness" by Fr. Leo Pyzalski, C.SS.R (also written before Vatican II). I recommend getting both because even though they address the same subject, they do so in different ways. I've used both since childhood even though they are written for adults.
I recommend reading "Holy Abandonment" by Lehodey first. It gives a good foundation to build from for discernment in particular circuмstances.
I hope you find the help you're looking for.