(seems like one of the easiest techniques)
http://www.mkyong.com/maven/how-to-include-library-manully-into-maven-local-repository/
Guide to installing 3rd party JARs (Apache Maven Project)
http://maven.apache.org/guides/mini/guide-3rd-party-jars-local.html
Maven External Dependencies (another valid technique)
http://www.tutorialspoint.com/maven/maven_external_dependencies.htm
Stackoverflow Link:
http://stackoverflow.com/questions/5692256/maven-best-way-of-linking-custom-external-jar-to-my-project
Adding external/custom jars into Maven project
Excellent link, especially "Installing jar into local Maven repository".
http://softwarecave.org/2014/06/14/adding-external-jars-into-maven-project/
In case content changes, screenshot of important snippet here:
