Assume that your directory structure is as follows.
<any folder ignored for the sake of simplicity>/MyFiles/Images/diagram-01.tex
<any folder ignored for the sake of simplicity>/MyFiles/Images/diagram-02.tex
<any folder ignored for the sake of simplicity>/MyFiles/Images/diagram-03.tex
<any folder ignored for the sake of simplicity>/MyFiles/Projects/Report-01/main.tex
<any folder ignored for the sake of simplicity>/MyFiles/Projects/Report-02/main.tex
<any folder ignored for the sake of simplicity>/MyFiles/Projects/Article-01/main.tex
Images contains diagrams that will be shared among many reports. Each report or article are saved in a separate folder to ease maintenance.
So you can, for example, import the diagram-01.tex from the first report's main.tex as follows.
% my first report
% main.tex
\documentclass{report}
\begin{document}
\input{../../Images/diagram-01.tex}
\end{document}
Or if the diagram has been converted to PDF format, you can import it as an image as follows.
% my first report
% main.tex
\documentclass{report}
\usepackage{graphicx}
\graphicspath{{../../Images/}}
\begin{document}
\includegraphics{diagram-01}
\end{document}
Here \graphicspath declares the path globally. By the way, \graphicspath can also be invoked as follows
\graphicspath{{../../Images/}{<any path>/}{<any path>/}{<any path>/}<...>}
where <...> represents that you can add more and more paths, but don't include <...> for sure.
Notes
If the file, i.e., diagram-01.tex that you want to import from within the main.tex is self-contained input file which can be compiled then you need to load docmute package in the main.tex such that main.tex will just import the contents sandwiched between \begin{document} and \end{document} of the diagram-01.tex.
\input{../../Files/myfile.tex}– Dox Jul 21 '14 at 15:12TEXINPUTS. However, you may also find the import package of value. – jon Jul 21 '14 at 15:39