Arrange you files so that you have one top file and then individual
files for each chapter. For example, thesis.tex (your top file)
contains
\documentstyle[12pt,suthesis,mymacros]{report}
% any personal definitions (or redefinitions) should be in
% mymacros.sty (or whatever you wish to call the file).
% No definitions should be in any of the subfiles (preface.tex,
% chap1.tex...) as definitions there can lead to some odd surprises.
% preliminary comments and information
\title{How to Write Theses\\
With Two Line Titles}
\author{John Henry Candidate}
\principaladviser{John Parker}
\firstreader{John Green}
\secondreader{John BigBooty\\(Another Department)}
\thirdreader{Jane Supernumerary} %if needed
% The following stops latex and allows you to select particular
% chapter(s) that you want latexed. When it stops, type in
% \includeonly{chap1,chap3}
% and only chap1 and chap3 will be processed. However, if you have
% previously processed chap2 it will know that chap3 does not start
% immediately after chap1. This allows page numbers to remain
% consistent (among other things).
\typein{includeonly command}
% other people prefer putting the \includeonly command directly in the
% top file and editing it as needed. If you type a carriage return or
% there is no \includeonly command, all the included files are processed.
\begin{document}
% each included file must be one that starts on a new page (hence
% chapter breaks are a good place to do this).
% place all text to be printed in the include files. Ideally if you
% typed \includeonly{} nothing should be printed.
% note that includes should only happen in this file.
\include{preface} % the file preface.tex
\include{chap1} % the file chap1.tex
\include{chap2} % the file chap2.tex
\include{chap3}
\include{chap4}
\include{chap5}
\end{document}