\documentclass[12pt]{article}
\usepackage{fixltx2e}%% the official fixes for LaTeX2e
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage[scaled=0.92]{helvet}
\usepackage{mathptmx}
\usepackage{courier}
\makeatletter
\def\verbatim@font{\small\normalfont\ttfamily}
\makeatother
\makeatother
\begin{document}
\section{The List Environment}
The 

\begin{itemize}
\item itemize-environment
\item enumerate-environment
\item description-environment
\end{itemize}
are all part of the \textbf{list-environment} of latex. 


\subsection{Vertical Linespacing}

Linespacing in standard list environments may sometimes too big. There
are several variables which controll this spacing:

\begin{itemize}
\item \verb/\topsep/ \hfill{}additional space before first and behind last
item
\item \verb/\partopsep/\hfill{}same as \textbackslash{}topsep when an empty
line is before the first and behind last item
\item \verb/\parskip/\hfill{}vertical space between paragraphs
\item \verb/\parsep/\hfill{}additional space between paragraphs for the
same item
\item \verb/\itemsep/\hfill{}additional space between different items
\end{itemize}

\subsection{Horizontal Linespacing}

\begin{itemize}
\item \verb/\labelwidth/ \hfill{}as the name says ...
\item \verb/\labelsep/\hfill{}additional space between label and text
\item \verb/\itemindent/\hfill{}indenting of the first line for one item 
\item \verb/\listparindent/\hfill{}same, but only for new paragraphs for
the same item
\item \verb/\leftmargin/\hfill{}same as in standard text environment
\end{itemize}

\subsection{Examples}

At first we set all variables to the value 0:

\begin{verbatim}
\setlength{\topsep}{0pt}
\setlength{\partopsep}{0pt}
\setlength{\parskip}{0pt}
\setlength{\parsep}{0pt}
\setlength{\itemsep}{0pt}
\setlength{\labelwidth}{0pt}
\setlength{\labelsep}{0pt}
\setlength{\itemindent}{0pt}
\setlength{\listparindent}{0pt}
\setlength{\leftmargin}{0pt}
\end{verbatim}

\begin{enumerate}
\item You can't put the \TeX{}-commands
before the environment, they will be overwritten when the \verb/\begin{<list-environment>}/-command. \\
On the other hand you can't controll horizontal spacing of the first
label in the first item, when you put the \TeX{}-commands behind the
first item, which is shown in this example for item 1. and 2. 
\setlength{\topsep}{0pt}
\setlength{\partopsep}{0pt}
\setlength{\parskip}{0pt}
\setlength{\parsep}{0pt}
\setlength{\itemsep}{0pt}
\setlength{\labelwidth}{0pt}
\setlength{\labelsep}{0pt}
\setlength{\itemindent}{0pt}
\setlength{\listparindent}{0pt}
\setlength{\leftmargin}{0pt}
\item Therefore you have to write your own environment with \\
\begin{verbatim}
\begin{<list-environment>}
-- all \TeX{}-commands --
\item my first bla bla textline
\item my first bla bla textline
\end{<list-environment>}
\end{verbatim}

This is possible in an existing list-environment in fact of the possibility
of nesting lists.
\begin{itemize}
\setlength{\labelwidth}{2cm}
\setlength{\labelsep}{0.1\textwidth} 
\item The first line with a 
\begin{verbatim}
\setlength{\labelwidth}{2cm}
\setlength{\labelsep}{0.1\textwidth}
\end{verbatim}
direct behind the \verb/\begin{itemize}/-command, means before the
first \verb/\item/-command
\setlength{\labelsep}{0pt}
\setlength{\itemsep}{-0.5ex}
\item A second line with a 
\begin{verbatim}
\setlength{\labelsep}{0}
\setlength{\itemsep}{-0.5ex}
\end{verbatim}
\setlength{\labelsep}{1em}
\item A last line with a \verb/\setlength{\labelsep}{1em}/ at the end of
the following \verb/\item/-command.
\item You have to remember that latex stores the values of the higher list-environment,
therefore all commands in this nested itemize-list are not valid outside
this list.
\end{itemize}
\setlength{\parskip}{1cm}
\setlength{\labelsep}{1em}
\item The last lines of the inner list are \\
\verb/\end{itemize}/\\

\begin{verbatim}
\setlength{\parskip}{1cm} 
\setlength{\labelsep}{1em}
\end{verbatim}
 
You have to remember that latex stores the values of the higher list-environment,
therefore all commands in this nested itemize-list are not valid outside
this list and vice-versa.
\item The last line ...
\end{enumerate}

\end{document}