if you have a valve on your fermenter make sure its closed before you pour you wort in. caught it pretty quick so only lost about a cup. but coulda been really messy
Don't start siphoning your beer from the fermenter to the bottling bucket and then walk away without checking that the valve is closed. I lost nearly a gallon of beer onto the kitchen floor before I came back to notice the leakage.
I've got to say I do this at some step on almost every other brew. I either leave a kettle ball valve or a bucket spigot open at some point; I've spilled beer, wort, sanitiser, cleanser, and water by this method. You'd think I'd learn but no...
This is why I like the red & white Italian spigots the most. If the lever's to the right,it's off. to the left,it's open. Quick & easy to spot. Besides forcing yourself not to rush through any step of your process. Haste does indeed make waste!