1. Let's get technical for a minute.
What we traditionally think of as knife sharpening is actually knife honing. When honing your knife, you're straightening out the steel of the blade of the knife (a dull knife is super bumpy which leads to ragged, hacking slicing). Actual knife sharpening requires removing/grinding/shaving bits of the blade off for a brand new, sharp edge. To sharpen requires a lot of practice or relying on professionals.
Hone your knife a few times a month, and you'll only have to sharpen your knives about once a year.
2. The tried and true honing tool: The honing steel
A honing steel comes with most knife sets, or you can buy one for a pretty reasonable price, like this one.
To hone, follow these steps (courtesy of Cooks Illustrated):
1) Place the honing steel vertically, with the tip firmly on your kitchen counter. Place the heel (bottom-most sharp edge) of your knife against the tip of the steel and point the tip of the knife upward. Target a 15-degree angle. If you're not good at eyeballing angles, pretend you're trying to slice off thin pieces of the honing steel.
2) Using light pressure and a consistent angle, slide your knife along the honing steel from top to bottom in a sweeping motion, pulling the knife toward you, getting the middle of the blade.
3) To finish, pass the tip of your knife over the bottom of the steel. Repeat the same motion of the other side of the steel/blade. You're targeting 4-5 passes on each side of your blade (for a total of 8-10 passes) for a sharper, straighter edge
Check out this video from Alton Brown for a good demo:
3. Use this hack if you don't want to buy a honing steel
If you don't want to splurge on a steel to sharpen, you can use the rough edge of a porcelain dinner plate to hone your knife.
Check out this tutorial from Chemistry Life Hacks:
4. If your knives are beyond honing, sharpening is the next step
If you've tried honing your knife and don't feel satisfied with your results, you can ship your knives to a professional.
Try one of these services:
Cutco will sharpen your blades for free, just pay for shipping ($9 for 1-10 knives).
The Edge Masters have prices that vary on type of knife, but you'll only pay $6-10 for most kitchen knives.
Razor Edge Knives offers a huge range of services, but for kitchen knives, you won't pay more than $20 a knife.
5. Want to sharpen yourself?
There are two real options for sharpening at home: wet stone and electric sharpeners.
Wet stone sharpening is the super bad-ass, super technical way to sharpen knives manually. I suggest a fair amount of research before attempting this yourself (or even taking a class).
Check out these videos to get your started:
Japanese Knife Imports:
If wet stones seem too much, you can try an electric knife sharpener. There are an easy, low-skill level way to get a crisp edge, but experts warn to use these with caution. They can take a ton of material off the edge of your blade, and this is super wasteful, especially if you have a super nice knife.
Before you buy, check out these recommendations from America's Test Kitchen:
SHARE with your friends and family that are always hacking away with dull knives.