I've found over the years that a number of things have helped me overcome doubt. First, when my faith is tested I lean more heavily on God. James 4:8 says: "Draw near to God, and He will draw near to you." The best way to grow in our faith is to abide in Christ as a branch on a vine, so his Spirit flows through us like sap. The more time we spend with God, the more real he becomes to us, and the more power he has in our lives.
Second, we need to stop treating our faith like a fragile object that must be stored away someplace safe. Although Christians talk about knowing the truth, we often act as if we fear the truth more than anything. It's okay to ask the hard questions lurking in our minds and let unbelievers challenge our faith, because God's truth can withstand our most intense scrutiny. As Christians, we have nothing to fear. So let's trust God that he is the rock of ages, including the scientific age. When we embrace all truth without fear, our faith will grow. God doesn't need our truth-twisting any more than we need a crooked attorney to defend us.
Third, God expects us to walk in faith. What are we willing to risk for God? Our money? Our reputations? Our lives? It's important to draw a distinction between walking in faith and putting God to the test. The same deed may be an act of faith by one person and recklessness by another, because the first person was led by the Holy Spirit. But often the Bible tells us very clearly what to do. For example, it tells us that if we give, God will give back to us. I've found that the best thing to do during times of financial uncertainty is to be generous. That is an act of faith. Will God keep his promise to provide? Yes, he will, and our faith will grow. When we choose integrity over popularity, we take a step in faith. God often rewards those acts of faith, but more importantly, we are building on an everlasting foundation that matters far more than his provision in this life.