This tiny booklet by MacArthur does a really good job of showing you what Scripture talks about when discussing God's will for your life. I'd recommend it to anyone seriously wanting to know what Scripture has to say about it.
You may want to jump and shout when you read the sixth principle for knowing when you have found God's will. The sixth principle is "Do whatever you want" as long as the first five principles are operating in your life. Read about all six principles to better understand what the psalmist means when he urges, "Delight thyself also in the Lord; and He shall give thee the desires of thine heart." (Psalm 37:4)