You have three options:
1) Create an AS 7 module definition which contains your jar file.
2) Deploy the jar directly in the standalone/deployments directory.
3) Deploy as an EAR and embed your library in the application archive.
In cases 1 and 2, you'll need to add a dependency definition to your SY application. You can find background info on that hear:
And here's an example of an application that uses option (2). The app declares a dependency on another deployment with 'deployment.OrderService.jar' :