Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
If someone is not a good speaker and does not have a lot of knowledge what can he do to call people to Allah?
Someone can be engaged in calling people to Allah through reflection and then giving advice to people based upon what he has reflected upon. He can spend his time and wealth, he can practically assist those engaged in dawah and he can make dua. He can distribute books and recordings to those who will benefit. He can call people to Allah on an individual basis and he can do so by showing good character to people generally.