One challenge that we all face with close-ups is sharpness. Three major problems can occur:
1.Depth of field gets shallower and shallower as you get closer and closer.
2.Camera movement during exposure is magnified when you are close to the subject.
3.Autofocus can focus on the wrong part of the scene. In fact, just a slight breeze can cause even manual focus to be off.
There is no one simple answer to these challenges. Here are some ideas:
1.Remember that depth of field is very limited when you are up close. Sometimes you have to shoot at f/16 or so in order to get any depth of field ... however ...
2.Since camera movement is really magnified when up close, you need to shoot at 1/125 sec. or faster (unless you are on a tripod, but tripods can have their own challenges for close work). That may mean you should use a wider f/stop, such as f/8. It is better to have the image sharp with less depth of field than fuzzy with theoretically more depth of field.
3.Sometimes the sharpest images come when the subject is sharp and the background is way out of focus. That contrast in sharpness actually makes the sharp object look sharper. I have often shot up close with the widest apertures for just this effect.
4.Since focus can be a problem try either shooting manually or locking focus with autofocus. With manual, set a focus at roughly the right spot, then do not change focus. With autofocus, lock focus at roughly the right spot, then keep pressing the button that locks focus. Now with either method, move the camera gently forward and backward until you see the key element comes into focus, then take the picture.
5.When shooting on a tripod, use Live View for focusing if you have it. Magnify the Live View image on your LCD so you can really see details and what is or isn't in focus.
Note: Outdoor Photographer editor at large and author Rob Sheppard teaches manyf outstanding online photography tutorials at BetterPhoto's digital Photography school, including Impact in Your Photographs: The Wow Factor and The Magic of F-stops: Choosing the Right Aperture.