Enable Remote Connections for SQL Server Express 2012

1. Run SQL Server Configuration Manager.
2. Go to SQL Server Network Configuration > Protocols for SQLEXPRESS.
3. Make sure TCP/IP is enabled.

Then,

1. Right-click on TCP/IP and select Properties.
2. Verify that, under IP2, the IP Address is set to the computer's IP address on the local subnet.
3. Scroll down to IPAll.
4. Make sure that TCP Dynamic Ports is blank. (Mine was set to some 5-digit port number.)
5. Make sure that TCP Port is set to 1433. (Mine was blank.)

If follow these steps, it's not necessary to enable SQL Server Browser, and only need to allow port 1433, not 1434

After all, go to Windows Service Manager and RESTART the SQL SERVER service to apply the changes.