One of the best tools for studying Scripture is a good concordance. Seeing how an author discusses a topic throughout a book or in his other books, or discovering how other authors discuss the same topic will help one develop a full theology on a given topic.
One book where it is particularly useful to use a concordance is Proverbs. Because chapters 10-31 are not arranged (in general) thematically, a concordance helps one to gather all the related verses on topics of interest.
Several years ago I compiled a brief (incomplete) concordance on many of the topics covered by Solomon in this book. You can download it as a PDF here.
[A brief overview of the book of Proverbs is also available here.]