How do you cut/file your nails like a professional?

I need to do my nails tonight, i have no time to go to the salon. how can i make sure not to cut it too short/not make it crooked etc? thanksHow do you cut/file your nails like a professional?
file into a sqqare shape and lightly file the edges so the side of your nail isnt sharp. Add a very light coat on color once its completley dried add a good heavier coat of color once that is dried add a clear top coat that will make it look shiner anad more polished. When appluing the nail polish make it as smooth as possible and dont leave brush strokes.