Be sure to grease the cups of your muffin pans well, brushing with a neutral oil like canola oil or spraying with non-stick spray. Use a mini offset spatula to help lift the muffins out of the pan. Toppings like cheese may cause the muffins to stick and you may need to use a little more force to unstick the edges close to the tops of the muffins because of this. Try to sprinkle the garnishes closer to the centre of the muffin tops and away from the sides. If all else fails, consider dusting greased muffin cups with flour before spooning the batter. This will help ensure they don't stick.