Here's How To Sharpen Your Knife Without A Knife Sharpener
Technically you really should be taking your knives to a sharpener, particularly if they're nice knives. But when it comes down to you, the cutting board and that tomato/squash/turnip you'd rather not slice off a finger for, your knife holds all the power.
Pick up an ordinary ceramic mug. That is your new knife sharpener you had in the cabinet all along, so say hello. Take your knife in your right hand and your mug, upside-down, in your left (or vice versa if you're a lefty). Inspect the bottom of your mug — see the thin ring of bare ceramic? That's your sharpening surface. Place the base of the knife blade on that ceramic part at a 30-40 degree angle, and firmly draw it against the grain towards you. (Note: metal blades only. No ceramic-on-ceramic action.)
Repeat four more times using the same amount of pressure, then repeat on the other side of the knife. This will push the carbon atoms into alignment, which results in sharpness. Return to the first side of the knife, then do three passes instead of four on both sides, then two, then one. Bam, freshly sharpened knife.
This isn't how you should sharpen your knives on a regular basis, however. Preferred methods include using a Japanese whetstone or taking the knives in for professional sharpening every few months. But when it comes to slicing that tomato or not slicing that tomato...refresh your edge a little, then slice it.
More Whatchamacallit on Food Republic: