Not knowing exactly what you’re doing. Everyone has been there and not everyone was wise enough to read a book or lucky enough to know someone who knows what they are doing to help. I was tossing together a list of the top things I wish I had known when I started and was looking for input. For the sake of this list I’m sticking to extract brewing because it seems that is where most people start. So far I have:
General yeast care: Includes pitching rates, temp control and leaving it do it’s thing for three weeks.
The importance of a hydrometer
The fact that secondary fermentation is not always necessary.
Cleaning then sanitize, sanitize, sanitize everything!
Aerating your wort
Correctly measuring stuff