On a natural nail, it is important to set the speed of the electric nail file to slow or medium. Too fast a speed could injure your client and above all, be sure to raise the tip regularly to avoid excessive heat on the plate. Also, never use carbide tips on a natural nail.
To shorten the nail, you will need a mandrel type tip + a fine sanding cylinder (240). Know that the conventional file will remain your best ally to create the desired shape. Then, if you want to remove the yellowed effect under the free edges, you can whiten them using a conical diamond or polishing stone tip.
When it comes to polishing, you will need a rather special bit. This tip is made up of several layers of superimposed leather, in order to create a good thickness. Using a cuticle oil spread on the plate, gently massage the nail with the tip on slow to medium speed. Always maintain low pressure and raise the tip frequently so as not to create overheating.