Yes, Surah Yusuf again.
“Say (O Muhammad): “This is my way; I invite unto Allah with sure knowledge, I and whosoever follows me. And Glorified and Exalted be Allah (above all that they associate as partners with Him). And I am not of the Mushrikoon (polytheists, pagans, idolaters and disbelievers in the Oneness of Allah).” [Surah Yusuf (12) :108]
This ayah tells us HOW we need to be doing dawah. Many people do dawah but is their way in accordance with this ayah? This is something that every caller (daee) needs ask himself or herself.
Shaikh Saalih Al-Fawzan explains the pillars of dawah as outlined by this ayah: The Pillars in Calling to Allah. Really great stuff.