Start with the ratio. One gram of coffee to sixteen grams of water is a dependable place to begin, so 20 grams of coffee makes a generous 320 gram mug. A cheap kitchen scale does more for your coffee than almost any other upgrade.
Grind just before you brew, aiming for something like coarse sea salt. Too fine and the cup turns bitter and slow to drain. Too coarse and it tastes thin and sour.
Heat the water to just off the boil, around 200°F. Rinse the paper filter with some of it first so the cup doesn't taste of paper, and so your dripper and mug start warm.
Pour about twice the coffee's weight in water and wait 30 to 45 seconds. This is the bloom: trapped gas escapes and the grounds settle in for an even extraction.
Finish with slow, steady circles, keeping the bed level. The whole brew should take three to four minutes. If it runs much faster, grind finer next time. If it stalls, go coarser.