Most home cooks should sharpen their knives at least twice a year, and much more frequently if they use their knives every day.
We recommend using a Sharpening Stone.
The best method by far. Not only will it give you the best edge, it also removes the least amount of material. With a fine enough grit, your knife should be able to take hairs off your arm when you've finished. Additionally—and I'm not kidding about the importance of this one—the act of sharpening your knife will help you create a much stronger bond with your blade, and a knife that is treated respectfully will behave much better for its owner. The only problem? It takes a little know-how.
That's why we would like to recommend reading the following article on seariouseats.com on how to sharpen your knives: