I know a lot of you already know/do this, but to those of you who don't - I know it has saved me more than once:

If you use SSMS (SQL Server Management Studio) - when connecting to a server, before you hit the "connect" button, under options, choose a color to represent which server you are connecting to. I personally use stoplight colors: red = prod, yellow = QA, green = dev....this way, it helps you realize what server you are connected to, minimizing our dreaded "oh shit" moments....lol

Hopefully this helps someone ☺