In order to have faith, one must have both hope and belief. We have already discussed hope, but how does one get belief?
One way is by being an eyewitness to a miracle:
Ma 27:41 Likewise also the chief priests mocking him, with the scribes and elders, said,42 He saved others; himself he cannot save. If he be the King of Israel, let him now come down from the cross, and we will believe him.
The chief priests and the scribes said they would believe Jesus if he were to save himself from death on the cross. Needless to say, they never got the pleasure of that experience, thank God!
Another example of this is found in the disciple Thomas:
Jn 20:24 But Thomas, one of the twelve, called Didymus, was not with them when Jesus came.25 The other disciples therefore said unto him, We have seen the Lord. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe.
26 And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.
27 Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing.
28 And Thomas answered and said unto him, My Lord and my God.
29 Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.
However, Thomas was fortunate enough to have his desire fulfilled.
Sometimes, a person does believe, but that belief is not strong enough. What is that person to do? We have the answer by example from the scriptures:
Mk 9:21 And he asked his father, How long is it ago since this came unto him? And he said, Of a child.22 And ofttimes it hath cast him into the fire, and into the waters, to destroy him: but if thou canst do any thing, have compassion on us, and help us.
23 Jesus said unto him, If thou canst believe, all things are possible to him that believeth.
24 And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief.
This man confessed his belief, and also his need for even stronger belief. He asked Jesus to help his unbelief. We see this requirement to ask God for what we need -- in this case belief -- illustrated in the following verse:
Mt 7:8 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened.
So it is promised that if you ask, you will receive. The father of the demon possessed son asked Jesus to strengthen his belief. He had to have some faith to do this, but by strengthening his belief, he had the belief necessary for the healing of his son. It took a little bit of belief to get more belief.