Praise be to Allah.
1 – I advise you to read the Quran a great deal, and listen to recitations of Quran and ponder the meanings of what you read and what you hear as much as you can. Whatever you cannot understand, ask the people of knowledge in your country or write to other scholars of Ahl al-Sunnah (Sunnis).
If you read a tafseer (commentary) on what you read, this will help you to ponder the meanings. One of the best and most concise Tafseers is Tafseer al-Sa’di (may Allah have mercy on him).
2 – You should remember Allah a great deal (dhikr), by reciting the dhikrs narrated in the saheeh ahaadeeth (authentic narrations)such as Laa ilaaha ill-Allah (there is no god but Allah), Subhaan Allah wa’l-hamdu Lillaah wa laa ilaaha ill-Allah wa Allahu akbar (Glory be to Allah, praise be to Allah, there is no god but Allah, and Allah is great), and so on. See al-Adhkaar by al-Nawawi and similar books.
Remembering Allah increases one’s faith and brings peace to the heart. Allah says (interpretation of the meaning):
“Those who believed (in the Oneness of Allah — Islamic Monotheism), and whose hearts find rest in the remembrance of Allah verily, in the remembrance of Allah do hearts find rest”
Observe regular prayer, fast and observe all the pillars of Islam, whilst also hoping for the mercy of Allah; put your trust in Allah in all your affairs. Allah says (interpretation of the meaning):
“The believers are only those who, when Allah is mentioned, feel a fear in their hearts and when His Verses (this Quran) are recited unto them, they (i.e. the Verses) increase their Faith; and they put their trust in their Lord (Alone);
Who perform As-Salaah (establish prayer) and spend out of that We have provided them.
It is they who are the believers in truth. For them are grades of dignity with their Lord, and forgiveness and a generous provision (Paradise)” [al-Anfaal 8:2-4]
It should be noted that faith increases when one obeys Allah and decreases when one disobeys Him, so continue to do that which Allah has enjoined, such as observing the five daily prayers in congregation in the mosque and paying zakaah (the poor-due) willingly, to purify yourself of sin, and as an act of mercy towards the poor and needy.
Keep company with good and righteous people so that they can help you to apply sharee’ah (religious teachings)and guide you towards that which will bring you happiness in this world and in the Hereafter.
Keep away from the people of innovation and sin, lest they tempt you and weaken your resolve.
Do a lot of naafil (voluntary) good deeds, and turn to Allah and ask Him for guidance.
If you do these things, Allah will increase you in faith and help you to catch up with what you have missed of good deeds, and make you more steadfast in adhering to Islam.