Using a pair of scissors is definitely an aquired skill. Some skills do not come naturally! When teaching children to cut, I make sure that I have the best performing scissors. Kids Fiskars are my favorite because, they make a nice clean cut, even if the skill of holding the scissors is a new mastery. The handles are also comfortable and well shaped for little fingers.
To begin, I sit behind and slightly off to the side of the prominent hand, place the scissors in the childs hand appropriately, then assisting hand over hand, move the blades up and down. I also model cutting as well. Then of course this activity has another skill - holding the paper that requires cutting. I use stiff paper such as construction paper or card stock, since it tends not to flop around and seems easier to hold at the proper angle to cut.
All this takes encouragement, dexterity and patients, as well as practice - practice - practice!
Today I put out a basket of scrap paper and my favorite scissors - the children seemed to enjoy their time manipulating the scissors until they got the desired technique!