The idea is simple, just prepare directory paths (to import both chapter files and images files) whenever you include a new chapter.

Main.tex

\documentclass{book}
\usepackage{graphicx}

\def\Include#1{%
        \def\ChapterPath{#1/}%
        \def\GraphicsPath{\ChapterPath Images/}%
        \include{\ChapterPath#1}}

\newcommand\IncludeGraphics[2][width=\linewidth]{%
    \includegraphics[#1]{\GraphicsPath #2}}    

\begin{document}
    \Include{Chapter-1}
\end{document}


Chapter-1.tex

\chapter{Chapter One}


\IncludeGraphics[width=0.5\linewidth]{Tulips}


Remarks:


Folder Chapter-1 is in Docoment-Root folder.
Chapter-1.tex is in folder Chapter-1. 
Tulips.jpg is in  folder Chapter-1/Images. 


Tips


If your TikZ code is not "linked" to the text with nodes, for example, then put such TikZ code into a separate, compilable input file. Use article document class plus preview to get a tight PDF output. You can also use standalone document class instead.
If you table is not long enough to span across multiple pages, then put it into a separate, compilable input file to get a tight PDF output.
It is better not to specify the image extension explicitly when invoking \includegraphics. 
Define macros for often-used materials and put them into a package such that you can change their definition later in one place and the changes effect the whole document.


How to work with large projects
I am hanging on this one since yesterday and was not able to find an example nor anything in the documentation --- maybe I am blind?

What i want is a matrix with border annotations BUT without the brackets (neither round nor squared nor curled, each of which have been discussed here). I also want to make the bordertext (A-E) bold and italic on the X and the Y axis... 

I have some code to construct the matrix as I have it right now:

\documentclass{article}

\def\VR{\kern-\arraycolsep\strut\vrule &amp;\kern-\arraycolsep}
\def\vr{\kern-\arraycolsep &amp; \kern-\arraycolsep}

\begin{document}

\LARGE
$\bordermatrix{
   &amp; A &amp; B &amp; C &amp; D &amp; E \cr
 A &amp; 0 &amp; 0 &amp; 1 &amp; 0 &amp; 1 \cr
 B &amp; 0 &amp; 0 &amp; 1 &amp; 0 &amp; 0 \cr
 C &amp; 0 &amp; 1 &amp; 1 &amp; 0 &amp; 1 \cr
 D &amp; 1 &amp; 0 &amp; 1 &amp; 0 &amp; 0 \cr
 E &amp; 1 &amp; 1 &amp; 1 &amp; 0 &amp; 0 }$

\end{document}

