It has surprised me that some people will use a tripod but not use mirror lock up nor a cable release. Well without a cable release you can use the 2 second timer, but without mirror lock up half the point of the tripod is lost. The slap of the mirror on any SLR camera is probably the largest negative effect on sharpness in any photo (depending on shutter speed of course and assuming the camera is steady). Do a quick test or look up many of the tests online, the mirror slap creates a lot of camera shake and reduces sharpness considerably. This video is quite good at demonstrating the difference. So, enable mirror lock up so you separate the mirror action from the exposure and shoot from a tripod using cable release for ultimate sharpness. And if you are me, try and remember to clean the lenses just once a year as well, that too helps with sharpness.
Now, the real trick and topic of this post is I recently begun to shoot handheld with mirror lock up enabled as well. It works better for stationary objects as you have to double tap the shutter button and with the mirror up of course you have a black viewfinder after the first click! But just learn to hold the camera steady in between clicks and you are fine and even handheld there is a large difference with the mirror locked up before exposure! Takes a bit of practice but it makes a large positive difference in sharpness for your handheld shots.