Response by Shaykh Maahir al-Qahtaani:
Ahlus Sunnah wal Jama’ah are in agreement that eemaan increases with obedience and it decreases with disobedience.
Allah says what is translated to mean:
As for those who believe, it has increased their Faith, and they rejoice.
In order for your eemaan to increase, you have to increase in your worship to Allah subhanahu wa ta’aala. Actions, like the recitation of the Qur’an and pondering over its meaning, standing in the last part of the night prayer, fasting during the day, obedience to your husband and not using your tongue for disobedience will increase your eemaan.
It is the removal of all of those things which are evil, and to purify yourself from those things, that will increase your eemaan. If a person wants to do a particular sin and their soul inclines towards that sin, if he leaves it off then, this is a cause for your eemaan to increase. If a person is commanded to do some type of worship and he does it seeking the face of Allah, then that increases your eemaan also.
From: The Rectification of the Muslim Women in the West with Q&A in London with Shaykh Maahir al-Qahtaani (Hafidhahullaahu ta'aala) - 02/12/2011