TEMPDB will automatically shrink whenever SQL Server is restarted, which might be most reliable way to do this, if needed. However, unless your TEMPDB is competing for storage with other databases, then there is no practical reason to shrink it ever. Ideally, TEMPDB should be allocated on a dedicated disk of it's own and just allowed to grow as needed.
"Do not seek to follow in the footsteps of the wise. Instead, seek what they sought." - Matsuo Basho