The right way to do this in Maven is to install it into a repository (remote or local).
However, there are circumstances that local repository is less preferable. For example, you run Maven on lots of machines and you don't want manually install it.
I just use the anti-pattern of checking JARs into version control in these rare cases. I don't even bother to install it to local repository because it adds another step and makes another copy of the JAR. I just use the JAR directly like this,
<dependency>
<groupId>local</groupId>
<artifactId>homeless-jar</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${basedir}/lib/homeless.jar
</systemPath>
</dependency>
EDIT: The ${basedir} is defined by Maven. It's the base directory of the Maven project, where your pom.xml is. My example wasn't clear. See this one,
<dependency>
<groupId>any-id</groupId>
<artifactId>any-name</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>${basedir}/src/main/lib/homeless.jar
</systemPath>
</dependency>