We strengthen our faith by: The careful reading of the Word of God, combined with meditation on it.
In order to grow in every grace of the Spirit, it is vitally important that we seek to maintain an upright heart and a good conscience, and therefore do not knowingly and habitually indulge in those things which are contrary to the mind of God.
So it is also particularly the case in order to grow in faith. If we desire our faith to be strengthened, we should not shrink from opportunities where our faith may be tried and therefore, through the trial, be strengthened.
Let God work for us, when the hour of the trial of our faith comes, and do not attempt to work a deliverance of our own.
"O that thou couldst dwell in the knowledge and sense of this! that the Lord beholds thy sufferings with an eye of pity; and is able, not only to uphold thee under them, but also to do thee good by them. Therefore, grieve not at thy lot, be not discontented, look not out at the hardness of thy condition; but, when the storm and matters of vexation are sharp, look up to Him who can give meekness and patience, can lift up thy head over all, and cause thy life to grow, and be a gainer by all. If the Lord God help thee proportionally to thy condition of affliction and distress, thou wilt have no cause to complain, but to bless His name.
"A state of mind that sees God in everything is evidence of growth in grace and a thankful heart." ~Charles Finney