How can I ensure that my Dawah activities will be acceptable by God ?

Being acceptable to God is a question that pertains to every deed, not only dawah work. No one knows whether his kalima was acceptable to God, or whether his worship was acceptable to God. The believer must perform these activities as a duty; whether or not they are acceptable to God will be known only in the world Hereafter. The only thing required is that one must read the Quran and Hadith to find out the commandments of God. And, when he is confident about a command of God, he must stick to it. As far as the question of acceptance to God is concerned, we can only make dua.