MORE STALLING: Before I talk specifically about the Rule of Thirds, I should say that all composition tips are merely suggestions and not requirements for a good photo. In one of my graphic design classes, my professor would always say that we need to learn the rules first, and then we can break them. I think that's so true in many disciplines--rules form a good foundation for creativity. Okay, get to the point, Jessica.
RULE OF THIRDS: To apply this rule, mentally divide your photo/frame into nine equally-sized sections using two horizontal lines and two vertical lines. The four intersections of these lines are guides for where your subject/focal point should be centered. I really prefer to use other people's photos to illustrate my point so that you can see how widely it is used, but I don't want to get in trouble with anyone, so I'll use my own. Here are a couple of visual aids to explain what I mean:
(Sorry about the dot-face, Katrina!)
You can also apply the Rule of Thirds when photographing landscapes. Try resting the horizon line along either the top or bottom third instead of right down the middle. It doesn't need to be exact, but it helps to decide on an emphasis--land or sky? It gives the viewer a little direction:
I hope that makes sense and that the lines aren't too distracting. :) Now that you're more aware of the Rule of Thirds, you'll notice it all over. For instance, painters, cinematographers and graphic designers make use of the rule all the time. Try it out and see if it adds some interest to your photos!