1. Tripod and cable release. It goes without saying for long exposures, but using a tripod can actually make many "normal" exposures noticeably sharper too. A good rule of thumb is that if the subject permits you to use a tripod, you should. (And if the exposure is long, be sure to incorporate a cable release or self timer to minimize camera shake too.)
2. Faster shutter speed. The faster the shutter speed, the less opportunities for motion blur and camera shake—two prime causes of blurry photographs. If sharpness is your prime concern, strike a balance between the widest aperture that permits a faster shutter speed, and the aperture that is itself the sharpest.
4. Increase the ISO. On its own, a higher ISO won’t help you make sharper pictures. BUT... if your choice is between a noisier sharp photo (from a high ISO and faster shutter speed) or a blurry low-noise photo (from a low ISO and slower shutter speed) choose the noisy sharp photo every time.
6. Understand how focus affects depth of field. If the depth of field of a given focal length, aperture and distance is three feet, then one foot of that depth of field will fall in front of the focus point and two feet will fall after. This rule applies on every lens at every aperture, give or take. So as a rule of thumb, pick a point of focus that is approximately one-third of the way into the total area you would like to be sharp, then stop down and check the DOF preview until you’ve got everything as sharp as you want it.