If you are running your user process locally on the server machine, you can bypass the shared server simply by using a direct connection. From a SQL*Plus prompt, issue the command
SQL> connect sys/oracle as sysdba
and you will get a dedicated server, because you have not specified a network alias that would go via a listener. All local connections, not just yours as sysdba, will do this. But most of your users will be coming in across a network through a listener. An application has no way of controlling whether it is using a shared server or a dedicated server, but as DBA you can control this through Oracle Net. If dispatchers and shared servers are available, by default every connection through the listener will use them. This default can be overridden by the connection details you specify in the client side tnsnames.ora file, configured either by hand or through the Net Manager.
Note that choosing a connection type is an example of something that can be done if you are using local or directory naming, but not with Easy Connect. Easy Connect will always use shared server if it is available.   _{Your Comment}