The best way to Da`wah (calling to Islam) is that stated by Allah (Exalted be He) in the following Ayah (Qur’anic verse):
Invite (mankind, O Muhammad صلى الله عليه و سلم) to the Way of your Lord (i.e. Islâm) with wisdom (i.e. with the Divine Revelation and the Qur’ân) and fair preaching, and argue with them in a way that is better.
Allah (Exalted be He) also says:
Say (O Muhammad صلى الله عليه و سلم): "This is my way; I invite unto Allâh (i.e. to the Oneness of Allâh - Islâmic Monotheism) with sure knowledge, I and whosoever follows me (also must invite others to Allâh i.e. to the Oneness of Allâh - Islâmic Monotheism with sure knowledge). And Glorified and Exalted be Allâh (above all that they associate as partners with Him). And I am not of the Mushrikûn (polytheists, pagans, idolaters and disbelievers in the Oneness of Allâh; those who worship others along with Allâh or set up rivals or partners to Allâh)."
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.