You know how they say to "learn from others' mistakes"? Well, let's help our fellow Nerdfighters out by stating some lessons we've learned so they might not make them as well. I'll start the list.
1) Don't use regular dish soap in the dishwasher. Unless you want your entire kitchen filled with bubbles (which may sound fun, but is a pain to clean up).
2) Don't walk while looking into binoculars. Especially when you're inside. Remember, objects are closer than they appear. (My little sister did this one. She ran into a wall and had two black eyes for a good week or so.)
3) Procrastination may pay off now rather than later, but it comes back to bite you in the long run.
4) When butting into someone's conversation, make sure you really know what they're talking about. (I've had many embarrassing moments when I butted in and promptly put my foot in my mouth.)
5) Don't put the Arby's sandwich wrappers in the microwave. They catch on fire.
6) Don't light a Klenex on fire unless you're prepared to deal with a flaming piece of cloth that doesn't blow out.
7) If you accidentally do #6, don't wait for your mom to find the singed carpet in your bedroom to tell her about the incident. She doesn't appreciate that.