Here some handy notes!
-n –20 => HIGHEST
-n 19 => LOWEST

$ ps axl

nice -10 <command name> and nice -n 10 <command name> will do the same thing (both the above commands will make the process priority to the value 10).

A major misconception about nice command is that nice -10 <command name> will run that process with -10 (a higher priority).

In order to assign -10 priority to a command then you should run it as shown below.

nice –10 <command name>

http://www.cyberciti.biz/faq/change-the-nice-value-of-a-process/http://www.thegeekstuff.com/2013/08/nice-renice-command-examples

Renice (change priority of a running process).

Example – put a PID to LOWER priority
$ renice 19 PID

http://www.cyberciti.biz/faq/howto-change-unix-linux-process-priority/