Truncate SQL Database Logs.

A backup software generally first take FULL backup and then INCREMENTAL backup where log file is truncated with the completion of INCREMENTAL backup. 

I want to truncate a large log file manually so want to check what should be on step 2, also want to confirm is below approach is correct for manual task ?- 

1. Take FULL backup of database. 

2. ___________________ Differential or Transnational Backup ?

3. Shrink Log file. 

Thanks

Vijay