One thing you should never do to a muffin mixture is use too much baking powder.
Using too much baking powder in a muffin mixture causes the muffin mixture to rise significantly and can cause the muffins to overflow in the oven.
Also avoid letting the muffin mixture batter sit for extended periods as it can alter how the final muffins come out.
And overmixing the muffin mixture batter results in tough and dense muffins, due to gluten development.
So avoid overmixing and fill the batter 3/4 full.
When making muffins you should also refrigerate the muffin batter before baking, especially if the muffin recipe uses baking powder, because it leads to a more flavorful muffin.
Refrigerating the muffin batter also allows the flour to fully hydrate and also allows the gluten to relax, and it can also make the muffin batter less sticky.
Although if your muffin recipe relies soley on baking soda for the leavening agent, then you should not refrigerate the muffin batter, because the baking soda will have already reacted and the batter will not rise properly.
The most common mistake when making muffins is overmixing the batter.
When you overmix the muffin batter, it crushes the air bubbles and ruins the fluffy texture.
And so to ensure you get light, fluffy muffins, mix the dry ingredients, with the wet ingredients until they are just barely combined and no more dry flour is visible.
Bakery muffins are so much better as they use higher quality ingredients, professional grade equipment, specific baking techniques and they also use more fat or richer dairy.
Bakeries also use carefully selected ingredients in their muffins and have precise control over their professional ovens, which can bake at a high initial temperature to create a taller dome.
Bakeries also use techniques like chilling the batter or resting the batter to improve the flavor and texture and they also often use butter or sour cream instead of cheaper oils for a richer taste.