So then faith comes by hearing, and hearing by the word of God.
Romans 10:17 (NKJV)
Two questions I often hear from lifelong Christians: "What must I do to grow in faith?" Sometimes they use another way of saying it: "Why can't I have faith like X or Y?". To these questions I always answer with another question: "Do you spend time in your Bible?" If the answer is NO, I suggest the person start doing it because the answer is there. If it's a YES, then I encourage him or her to persevere.
You will probably say my answer is rude. I will agree with you, but what does the Bible teach us about faith? It says, "Faith comes... from the word of God." Thus, the only way to understand faith and grow in faith is to hear (pay attention to its teaching) and know (study) the word of God. Of course, trials are also part of it, but they only serve to test the authenticity of our faith in God. Many people say they have faith, but when they see difficulties and obstacles, they begin to doubt. Why? Because what they know is what they hear from others, but they don't know the facts of God, revealed in His word.
I would like to tell you this, if you want to have a stable faith that does not waver, start studying your Bible, meditate on it day and night. I am not saying that this knowledge will automatically give you the faith you want to have, but it will help you to walk in the will of God and rely on Him, for His word will reveal to you His mighty deeds and His will for your life.