A glass nail file can help create smooth nail edges when used gently and with control.
File gradually
Decide on your desired length and shape, then work slowly rather than removing too much at once.
Use light pressure
Hold the file comfortably and use gentle movements along the edge. Avoid pressing hard or repeatedly filing the same spot.
Finish and store
Check the edge for rough areas and make small adjustments. Store the file in its case when finished.