What lens are you using? Generally, kit lenses or slower zooms (f/3.5-5.6), have a sweet spot of around f/8 or f/11. Your DoF (depth of field) won't be as extreme as if you were to use f/16 or f/22, but the in focus areas will be sharper. Wide open, lenses get chromatic aberrations or "colour fringing" and aren't too sharp, and closed to their smallest aperture such as f/22 they suffer from diffraction, when the light entering the lens gets bent in odd ways, and you get a softer image. On lenses with a larger maximum aperture, such as an f/1.4 or f/1.8 lens, your sweet spot will be something like f/4 or f/5.6, but again, if you stop down too much you'll have to deal with diffraction.
I shoot most landscaped at f/11 on my 16-85 f/3.5-5.6 zoom, it's sharp and gives me the DoF that I need. With my 35mm f/1.8 lens, unless I'm doing astrophotography where an open aperture is needed, I shoot mostly at f/5.6, the lens' sweet spot.
If you need longer exposures, as opposed to stopping down to f/22 I'd recommend purchasing a good quality and sharp neutral density filter. These will run anywhere from $50 to $150 depending on which filter you buy and what lens you use it for. These filters let you use apertures like f/5.6 where your lens will remain sharp, but they'll cut down the amount of light reaching the lens, and you'll be able to shoot at slower shutter speeds to get the same exposure. They're great for blurring water, or shooting moving objects that you want to blur in broad daylight.
I generally shoot landscapes by stopping my lens down from f/5.6 to f/11, placing the camera on a tri-pod and making it level and using my remote to lock the shutter up and take the exposure. Turning VR/IS off will also help most of the time. This will guarantee no motion blur at all.
Care to post some sample photos of your problem? That may help.
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams