Some people say that one way we can know we are in God's will, is when we are prospering, since God brings blessing. Let's have a quick look at this verse:
This is the kind of verse that sports people often put on their gear or person when competing (eg. Evander Holyfield) and others preach from or quote from to make a declaration that the world is their oyster.
Taking a look at its context lets look at the 2 verses before
Php 4:11b-13
"I have learned to be content whatever the circumstances. I know what it is to be in need and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want. I can do all things though him who gives me strength"
So prosperity alone is not a guide. Also check Jesus: the son of man has no place to rest his head...