Praise be to Allah.
There are several means of increasing faith:
The first means is learning about Allah through His names and attributes. The more a person learns about Allah through His names and attributes, the more he will increase in faith, without a doubt. Hence you find that the scholars who know more about the names and attributes of Allah than others do, are stronger in faith than others in this regard.
The second means is looking at the signs of Allah in the universe and the signs of sharee’ah (i.e., verses of the Qur’aan and miracles of the Prophet (peace and blessings of Allah be upon him), etc.). The more a person looks at the signs of Allah in the universe, the more he increases in faith. Allah says (interpretation of the meaning):
“And on the earth are signs for those who have Faith with certainty.
And also in your ownselves. Will you not then see?” [al-Dhaariyaat 51:20-21]
The verses which indicate that are many, I mean the verses which indicate that by pondering and thinking about this universe, man can increase in faith.
The third means is doing many acts of worship, for the more acts of worship a person does, the more he will increase in faith thereby, whether those acts of worship involve words or actions. So dhikr increases faith in quantity and quality, and prayer, fasting and Hajj also increase faith in quantity and quality.