Tuning a violin: pegs and fine tuners
For small adjustments, use the fine tuners on the tailpiece: they are more precise and won’t make the peg slip. Keep the pegs for large changes, pushing the peg gently inward as you turn so that it holds.
Tune the 2nd string first, the one the orchestra tunes to, then the others. After changing strings, check that the bridge is still standing straight.
Fiddle cross tunings
In traditional music (old-time, Irish, Cajun), fiddlers sometimes retune so that the open strings ring along with the melody: AEAE and GDGD tunings make the violin resonate in certain keys.