LaTeX: indent from second line
Similar to Ricibald's answer but simpler (it wasn't clear to me in his post which length was doing the job). I was using this for a bulleted list to indent each line after the first:
\begin{list}{}%
{\leftmargin=1em \itemindent=-1em}
\item
\item
\end{list}
Depending on why you want to do this, you might be better off using the built-in TeX support for hanging indentation, which the hanging package sugars. If it's a one-off, use the package, but if it's built in to some other layout, the package might just confuse things. Up to you.
The \hangindent dimension gives the size of the indentation, and the \hangafter number indicates when that indentation should start or stop. If the \hangafter number is positive, then indentation starts after that number of lines; if it's negative, then it starts immediately and stops after (minus) that many lines.
These apply only to the immediately following paragraph. The hanging package handles this by using \everypar. That's an occasionally problematic technique, which is why the package includes a 'word of caution' about it.
\documentclass{article}
\parindent=0pt
\parskip=\medskipamount
\begin{document}
\hangindent=2em
\hangafter=2
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Proin eu tempor velit. Fusce accumsan ultrices fringilla. Praesent
sed odio mi. Mauris non ligula turpis. Duis posuere lacus nec diam
interdum dictum suscipit magna molestie. Vestibulum nibh dolor,
interdum eget rhoncus ut, sodales eget justo. Morbi blandit lorem
sit amet nulla egestas aliquam. Nunc pharetra est at nibh ullamcorper
in commodo erat dignissim. Cras et suscipit enim.
\hangindent=2em
\hangafter=-2
Nunc adipiscing ligula at ligula egestas id ullamcorper felis luctus.
Aliquam tincidunt turpis sed eros pellentesque iaculis. Nulla
imperdiet cursus enim condimentum congue.
\end{document}
Negative hanging indentations in LaTeX are most easily handled with the hanging package.
Edit: Fixed the broken link.
\hangindent=\parindent
\hangafter=1
\noindent
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Proin eu tempor velit. Fusce accumsan ultrices fringilla. Praesent
sed odio mi. Mauris non ligula turpis. Duis posuere lacus nec diam
interdum dictum suscipit magna molestie. Vestibulum nibh dolor,
interdum eget rhoncus ut, sodales eget justo. Morbi blandit lorem
sit amet nulla egestas aliquam. Nunc pharetra est at nibh ullamcorper
in commodo erat dignissim. Cras et suscipit enim.