Macro photography is the art and science of photographing subjects up close, typically flowers and insects. It is not for the faint of heart; it takes loads of patience!
Lighting: If you are a fan of photographing flowers and macro nature, try shooting in shaded areas or on overcast days. This will help you avoid harsh light and shadows on your subject. But if you do find that perfect subject in full sun, you can always use a diffuser to soften the light. A diffuser is an opaque piece of fabric that helps cut the harshness of light. Get yourself a 22" 5-in-1 reflector; the base will be the perfect diffuser!
Depth of Field is crucial in Macro Photography. We want a shallow DOF to make the subject pop, but we also want to make sure the whole subject is in focus. Macro lenses tend to have a blurry background regardless of the aperture, but using too big of an aperture can blur too much. When shooting in Aperture Priority (A or AV) try sticking with a medium f-stop like 5.6 or 8.
If you've got one, a DOF preview button is a huge help! It's a little button near the base of your lens on the camera (not the lens eject button but close to it), tapping that button will show you how much of your image will ultimately be in focus.
Macro Lens Alternatives: You don't need a macro lens to get close up shots! There are many less expensive options such as close up filters or extension tubes as well as the technique of 'Poor Man's Macro,' used here. If you set up your exposure first and then disconnect your lens, (any lens!) you can turn it around and hold it up against your camera to create a macro lens! (Be warned, this does increase your chances of collecting sensor dust!)
All of the alternatives to a macro lens; extension tubes, and close-up filters, require even more patience than usual and the best focusing tips are to simply move back and forth in regard to your subject until you see it become sharp. In the case of the filters and tubes it can also be helpful to zoom in and out if using a zoom lens. If you have trouble focusing, you probably need to get closer!
Consider using a tripod. A tripod will allow you to slow down and carefully compose your images. It will also give you the option of shooting longer exposures, however if you have long exposures you need to be in a controlled macro environment; no wind or motion! Remember to always turn off your lens's Image Stabilizer when using a tripod.
Focus Modes: There are a few ways to allow your camera to focus on a subject. While still subjects like portraits and flowers fare well with the One Shot or AFS mode, animals are unpredictable and may move quite a bit; in this case you may want to try shooting in Continuous or AFC mode, which will automatically focus on the moving subject. Always remember to turn off image stabilizers when using a tripod. Accompany it with a remote or cable release and try using live view to compose and aid with focus.