Then a leper came forward. He knelt before him and said, «Sir, if you want to, you can make me clean».
Today we see an example of how we should ask things to God: with a strong faith. There is no better argument than this: "If you want, you can make me clean" And, because the Lord loves us infinitely, He has no choice but to answer: "I am willing, be clean". But to God we must ask "well” and, in addition, only "good things".
-- To ask for good things, which are worth: this is not so easy! More often than not we ask what we "like" the most, but not "the best". Want a trick? ask for the needs of others. The Virgin Mary did so and it worked out very well.