SQL Server 2012 database log file is too large, how to shrink?

Recently discovered Web sites are inaccessible because the database server disk has no more space left. The log file was found to be 70%, and shrinking the log file failed.

The reason for the online lookup is that no backup cannot shrink the log file.

A temporary solution:

Back up the transaction log, and then shrink the log file. (You can also shrink a log file after a full database backup)

A long-term solution:

Make a maintenance plan, back up the database regularly, and shrink the log files.

SQL Server 2012 database log file is too large, how to shrink?