There are so many little details! Make sure that you hit your target temperatures for mashing, and make sure you know what temperatures you want for the desired result. Be sure your water is good, since your water makes up the vast majority of your beer. This includes mineral composition and softness. Make sure you come up to around 170 degrees for mashout, and keep your temperature up there for sparging. Definitely make sure that you use good ingredients. Use something like maris otter for pale malt, or whatever taste you prefer. Get good yeast and use a really kickin' yeast starter. Oxygenate your wort well prior to pitching. Keep fermentation temperatures constant. Know what works best for your system.
There are many details that you can watch, but most importantly, brew what you like to brew, and brew what you enjoy best. This should be fun above all else. There's not much point in minding all of the little details if it starts to feel like work and less like a relaxing and enjoyable hobby.