Water temperature matters more than you'd think. Aim for 200°F (93°C). No thermometer? Boil your water, then wait 30 seconds. That gets you close enough. Water that's too hot makes coffee bitter; too cool makes it sour and weak.

Grind size is the other big variable. For pour-over, you want something like sea salt—not too fine, not too coarse. If your coffee tastes bitter, go coarser. If it's sour, go finer. It's a simple fix that changes everything.