Paul tells us in 2 Corinthians 9:6-7 "But I say: He who sows sparingly will also reap sparingly and he who sows bountifully will also reap bountifully. So let each one give as he purposes in his heart, not grudgingly or of necessity; for God loves a cheerful giver."
What does God want? - Well, that's simple... He wants our hearts to be fully devoted to Him. The greatest thing that we can give to God is our hearts.
We often associate this verse in 2 Corinthians with giving up for the collection plate when it's passed around on Sunday mornings. But I think we can relate it to anything that requires us to give - our time, our attention, our hearts, etc... Paul also tells us in Phil. 2 to do everything without complaining and disputing.
Like I said, God wants our hearts. He doesn't want hearts that are half devoted to him and half devoted to the world - He wants us to be FULLY devoted. And He deserves that from us. We need to make sure that we're giving God what He wants.