Widows and Orphans

Widows and orphans are typically considered bad style. While you may not want to completely forbid them in shorter documents like papers, avoiding them in a thesis etc. is mandatory.

An automatic layout that tends to completely avoid widows and orphans can be achieved by adding:

\clubpenalty = 10000
\widowpenalty = 10000
\displaywidowpenalty = 10000

A milder form that is more suitable for space constraint documents such as short papers is:

\clubpenalty = 150
\widowpenalty = 150
\displaywidowpenalty = 150

Some more information for particular document styles can also be found here.