Hold the violin in playing position
Turn on a tuner or tuning app
Tune the A string first to 440 Hz or your preferred reference pitch
Use the fine tuner on the A string if available
If needed, adjust the peg for the A string slowly and carefully
Tune the D string to match the A string at the correct interval
Tune the G string to match the D string at the correct interval
Tune the E string to match the A string at the correct interval
Check each string again after tuning all four strings
Make small adjustments until all strings are in tune
Recheck tuning after playing for a few minutes