The sharpness is one of basic factors of a good picture. Factors, which affect it are generally well known – exposure time equal to the inverse amount of the focal length, continuous release control, stable position of the photographer including firm camera holding...
There are also two other factors, which are not so discussed but can also have an indispensable effect for the picture sharpness:
1.Lens with a high lens speed – high-quality lenses are quite expansive. Photographic technology made a big progress and that is why you can sometime hear: „Why should I buy an expensive lens with a high lens speed if I can reasonably adjust ISO without a big noise increase, i.e. quality decrease? If we do not speculate about other aspects ( depth of field for example ), it could be right.
2.AF points – according to the type of camera it can have from 3 to 51 ( generally ) of them. Mainly in middle class cameras, probably in an effort of producers to save money, all points do not have the same sensitivity. Some of them are more sensitive for horizontal, some of them for vertical edges ( and their shape corresponds with it – look to the picture ).
Have a nice light!