Homebrewing is about learning as you go. That means mistakes. Learn from the long list of ours.
Don't ever assume fermentation is complete.
Measure it with a hydrometer. Always. Bottling too early can lead to some serious problems with over carbonation, since it essentially rouses the yeast back into activity if it had gone dormant before fermentation was complete.
Don't airlock a closed system fermentation until it's clearly done frothing.
It can explode. If the glass doesn't shatter (and it can), the airlock may shoot off and hit you in the face, spraying wort, yeast, and hops all over your kitchen and giving you a fruit fly problem for weeks. There's still hops stuck on my ceiling.
Don't dry hop without a sachet or muslin bag.
The broken up hop pellets will end up in your beer unless you filter them out, which can be difficult. You don't really want to chew on a hop while drinking your IPA... or do you...?
If you're going to leave beer to condition for an extended period of time, make sure it's completely airtight and in a dark, stable environment.
Vinegar is great, but not to drink straight.
Make sure you know the spices you're using.
Some spices are very, very potent. Dill is one of them. Star anise is another. They pack a whallop. Do your research on recipes beforehand, and read what other people use before trying them yourself. Don't substitute one spice for another because they seem similar, they often have very different characteristics.
