When dealing with close-ups in photography, don’t forget that the zone of acceptable sharpness in any image gets smaller and smaller as the magnification gets bigger. This is so much so that you may find virtually no depth of field in your images when working at very close-up ranges.
So therefore you need to be more careful than ever to focus accurately on the main point of your image. Depth of field is dependent therefore not only on magnification but also aperture as it would be in normal photography.
Where possible and if light levels allow, it would be useful to determine your focusing and therefore your depth of field when the lens is stopped down as much as possible. Although tables do exist in order to determine the depth of field, they really are no substitute for looking at the subject through the lens itself.
When your images get to more than half life size, even a small error in focusing can cause problems with the resulting image. With some cameras the actual image you see in the viewfinder is not the one that you see on the final produced image.
Some photographers will look at the scene with the aperture one or even two stops wider than the aperture that they will take the shot at. This will not equate with the actual image outcome but will ensure that your depth of field is more accurate as you’ll be able to see the image more closely and in more detail.