Don’t overmix the batter. Overmixing can produce tough and deflated muffins. Stop mixing just when streaks of flour are no longer visible, some lumps are okay.
Fill muffin cups a generous 3/4 way full. Filling any higher will cause them to spill out of the cup and produce a flat-topped muffin, but filling them too low doesn’t give the muffin enough batter to rise to nice domed height.
Don’t overbake. Muffins are done when the center springs back when gently pressed.
Remove muffins from the pan as soon as they are just cool enough to touch. Do not let them cool completely in the pan or they will be overbaked and soggy on the bottom. I usually let them cool in the pan only 1-2 minutes.