Using the titlesec package you can use \titlespacing* you can change the spacing before and after the title; the syntax of the command is:
\titlespacing*{<command>}{<left>}{<before-sep>}{<after-sep>}
(there's an additional optional argument, but it's not important here). <left> increases the left margin; <before-sep> controls the vertical space before the title; <after-sep> controls the vertical space after the title. (Please refer to the package documentation for further information). A complete example:
\documentclass[10pt]{book}
\usepackage{titlesec}
\usepackage{lipsum}% just to generate text for the example
\titlespacing*{\section}
{0pt}{5.5ex plus 1ex minus .2ex}{4.3ex plus .2ex}
\titlespacing*{\subsection}
{0pt}{5.5ex plus 1ex minus .2ex}{4.3ex plus .2ex}
\begin{document}
\chapter{Kapitel 1}
\lipsum[4]
\section{Einleitung}
\lipsum[4]
\subsection{Motivation}
\lipsum[4]
\end{document}

I used ex (approximately the height of an "x" in the current font) as the unit for the lengths used, but you can use instead any other valid LaTeX unit (cm, in, mm, pt, among others); you can also use multiples of predefined lengths such as \baselineskip:
\titlespacing*{\subsection}
{0pt}{2\baselineskip}{3\baselineskip}
I used ex since in this way the space is font-dependent. If you want to change the formatting of the titles, you can also use the same package and its powerful \titleformat command.
{}) or hit Ctrl+K. – Claudio Fiandrino Apr 14 '13 at 13:05\section? – Gonzalo Medina Apr 14 '13 at 14:55\titlespacing*{\section} {0pt}{3.5ex plus 1ex minus .2ex}{8.3ex plus .2ex}
\begin{document}
\chapter{Kapitel 1} \section{Einleitung} \subsection{Motivation}
\end{document}`. Is it something like that what you need?
– Gonzalo Medina Apr 14 '13 at 19:21Ok I think sectsty and titlesec don't like each other. I just tried both together in a simple code, and the titlespacing didn't work again, so this is the problem I think.
– abdu Apr 14 '13 at 20:07\\incorrectly. – Gonzalo Medina Apr 14 '13 at 21:28