A closer look:
Prove - to test, to ascertain, to try, discern.
will - desire, pleasure, inclination, determination (as in decision).
First things first, we needed "God's will" yesterday. Attaching the phrase God's will to any of our decision doesn't mystically sanctify that decision to be so. Worse, it takes God's name in vain (which is no small thing). To be certain, God has a will. He has one for everyone of us (see 2 Pet. 3:9 for an example). But it isn't so that He divinely reveals it only at certain points in our lives like the high mountain top experiences of graduation, marriage, vocational calling or career decision, relocating because of job opportunities, etc. He does reveal His will to us. He does so every day and it is our responsibility to prove it. It is our responsibility to obey God, and when we surrender of our will to His, our minds are renewed. Renewed minds are required for ascertaining God's will. God's will is good, acceptable, and perfect because it reflects on the person of God Himself. If you want to know God's will, then allow Him to renew your mind. It isn't important to say: "God's will for my life" as it is to say: "My life for God's will." Knowing God well is knowing God's will.