The best dialogue starts with the use of proper recording techniques during production. The more time and effort you put into getting good sound during production, the less time you need to put into improving it in post-production. Sometimes just switching locations, say from a busy street to a quiet one, can improve the production sound quality and this may avoid the need to do ADR (Automated Dialogue Replacement). Poor production sound is one of the most common technical problems with no and low budget films.