Lyle Schaller is a great author and church consultant. Read the other books on assimilation and you will find that they cite Schaller and use his ideas extensively. He has lots of other great books too.
Lyle Schaller's book Assinilating New Members is a good practical process in assimilating new member into the fellowship of any church congregation. He discusses the reasons people do not join a church. He helps the church evaluate who they are and what they do to either exclude or include new members. This little book is worth having in one's library.