Add
\usepackage{setspace}
\doublespacing
to the preamble. The whole document will be double-spaced including bibliography. Footnotes, figures, and tables will still be single-spaced. If you want a part of the text still be single-spaced, include the part in the environment:
\begin{singlespace}
\end{singlespace}
If you want to have other spacing effect for a part of the text, you can use the environment:
\begin{spacing}{space}...\end{spacing}
. For example, to reduce the linespacing in the bibliography and table of contents, you can use the following command
\begin{spacing}{0.9}
\tableofcontents
\end{spacing}
...
\begin{spacing}{0.9}
\bibliographystyle{plain}
\bibliography{refs}
\end{spacing}
The other two commands provided by the
setspace
package are
\singlespacing
and
\onehalfspacing
You can also change the other spacing by using the \setstretch command, e.g. \setstretch{1.8}. To get single-spaced, one-and-half-spaced, and doublespaced effects, you can also use \setstretch{1}, \setstretch{1.5} and \setstretch{2} respectively.