In order to get close to the subject, you need to be able to focus close. If you're using one of the kit lenses, you won't be able to get much closer than a foot or two.
In order of decreasing cost:
- Special macro lenses are designed to focus closer, as close as a couple of inches, but they cost more.
- Extension tubes fit between the camera and other lenses, allowing the lens to focus closer.
- Close-up adapters fit in front of the lens, also allowing closer focus.
One major consideration with any type of close-up photography is lighting. Having the camera close to the subject tends to block out light. Two possible ways around this are: a tripod or other support, and an additional light source such as an external flash unit.