In some situations you may not see the target Mac listed under Shared in the finder. In addition, this tip is specific for situations in which the Screen Sharing service is known to work.

Connecting is similar to accessing a Samba network share. In this example the target machine’s IP address is 192.168.1.5:

1. On the Finder menubar select Go
2. Choose Connect to Server
3. In the Server Address box type vnc://192.168.1.5 [or your target machine IP]
4. If you want to save it under Favorite Servers click the plus button
5.  Click Connect
6. Provide the appropriate authentication credentials

A while back I posted another tip about enabling and disabling Screen Sharing from a terminal, which can be used to change the status of Screen Sharing remotely via an SSH connection.