Sir Revert2001, Alhamdulillah its great to know that you are amongst the 'thinking' ones, and I suggest you please please read Hayatus Sahabah (the lives of the sahabah) its the ultimate book on how the sahabah gave daawah, its available in English 2 volumes: 1 2 and Sir, we aren't just calling towards Oneness of God, we are calling towards complete Deen, for which a Da'ee himself/herself should be in as much in sunnah as possible. do read about maulana kaleem siddiqui if you can...