-Do not use a remote probe thermometer that is designed to monitor roast meat in the oven. The probe to wire connection is not waterproof and you will eventually short the connection. I went through 2 $20 probes before getting smart and reading about it on here.
-Temperature indication is important during extract brewing but critical for AG brewing (which is not any more difficult than extract - just a little more time consuming).
-Temperature indication/control during fermenting is critical.
-Glass thermometers are ok IF - you are using the correct range and IF it is NOT a floating thermometer. i.e. Lab Thermometer. You pay for accuracy/lower price with fragility. Acurate, rugged, designed for high temp liquid remote probe/non-remote probe digital thermometers are expensive but worth it.
-Not all digital thermometers are created equal. Do some research before you purchase or you will be repurchasing thermometers.
-During fermentation and depending on the beer and setup (carboy vs. bucket), you may encounter vigourous fermentation. Have a blowoff tube setup nearby (or instead of the airlock). Last night I walked by my Hefeweisen in the carboy and it was hissing at me pretty loudly. I immediately sanitized my blowoff tube and replaced the airlock with it. (A loud release of CO2 informed me that yes, I was about to have a nice burp of kraussen everywhere).
-Be wary of where you brew if you use a propane burner. Carbon monoxide dangers are very real.
-The more organized you are the more fun the brew day can be. Lay out your ingredients, brewsheet (if using), equipment and sanitation bucket.
-Sanitation is beerlyness
-Finally, if you miss you temps, times, forgot to sanitize something and realize it later, you will still most likely have great beer to drink. All these things we do that sound ridiculous at times is to just increase the chances (already high as it is) of getting a great beer.
-Oh and ask a lot of questions but use the search function first. There are a lot of threads buried on these forums with great info. Can't sticky them all.
Rob