Within the <configuration> node, add the following. Note if the log4net section already exists this needs to be appended to it instead,
<log4net>
<appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender" >
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%ndc] -
%message%newline" />
</layout>
</appender>
<appender name="FileAppender" type="log4net.Appender.FileAppender">
<file value="log-file.txt" />
<appendToFile value="true" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger
[%property{NDC}] - %message%newline" />
</layout>
</appender>
<root>
<level value="ALL" />
<appender-ref ref="ConsoleAppender" />
<appender-ref ref="FileAppender" />
</root>
</log4net>
