Always walk around the aircraft before strapping in.
Always do a hover check....if it isn't right to hover....it isn't right to fly.
Inflight change in vibration levels....land and find out why then continue the flight if it is safe.
If the Maintenance Release is not signed....the aircraft is U/S. (If the engineer/mechanic has not signed his name......he isn't responsible for what happens if you do....but you are.)
"I think I can."....and "Watch this!" kills pilots.
Never...Never...Never...do spontaneous low level flying. Always....always...always do a Recce/Recon first. Then have your fun.