I will be the first to admit that keeping my nails in tip-top (sorry, bad pun) shape is a difficult goal for me. A few years ago as I was doing a little shaping action of my own, my friend, who supplements her income by working as a part-time manicurist, laughed out loud. "It's called an emery board, not a saw," she said.
So, apparently, I was doing it wrong. She told me all about the "short, short, long" technique, and I've never looked back to my overly aggressive tree-logging ways.
In order to achieve smoothly filed nails, it's best to start off by using a fine grit emery board, which is very gentle for natural nails. Starting on one corner of your nail, moving towards the center. File in a "short, short, long" motion, using the "long" motion to blend, smooth, and help mold your nails into the shape you desire. Then, repeat this step on the other corner.
Just remember to always file in one direction, otherwise you'll get jagged results. It's pretty simple once you get the hang of it — and your polish will last longer, too.