Sacred Citation & SourceAllah says: "Surely in the remembrance of Allah hearts find rest" (13:28) and "Remember Me, I will remember you" (2:152). The Prophet ﷺ said: "The example of the one who remembers his Lord and the one who does not is like the living and the dead" (Bukhari 6407).
Sacred Citation & SourceSimple forms of dhikr: "SubhanAllahi wa bihamdihi, SubhanAllahil-Azim", two phrases light on the tongue, heavy on the scale, beloved to the Merciful (Bukhari 6406, Muslim 2694); the tasbih after each prayer (33 SubhanAllah, 33 Alhamdulillah, 33 Allahu Akbar, Muslim 597); istighfar; sending blessings on the Prophet ﷺ; and the Qur'an itself.
A small, regular habit is better than a rare long one: choose a few minutes in the morning and evening, and say the words with presence of heart. These are matters of the heart, not of rulings: take what helps you act and ask a qualified teacher if you are unsure.