How are you taking your shots? There are a variety of factors that affect the clarity of a shot that you might want to work with. Lighting, aperture, shutter speed, and the type of thing you are shooting all play into how your shots end up looking.
Lighting and Aperture
First off, lighting. If you are regularly shooting in dim lighting, and you have a slower lens (i.e. f/4 maximum aperture or tighter) you might really need to consider getting a better lens. Something that has a faster maximum aperture, such as f/2.8 or f/1.4. Wider apertures (smaller numbers) allow more light in, so night shooting or photographing indoor sports greatly benefit from wider apertures.
Second, you might look at what shutter speed you are using. A general rule of thumb is that a shutter speed at least as fast as one over the focal length of a lens necessary to take a "stable" shot. If you have an 18-70mm lens at 70mm, then you would need a minimum shutter speed of 1/70 to take a stable shot. In low light, that may be too fast to capture a bright enough shot with an aperture of f/5.6. On the other hand, at 18mm, you would only need a shutter speed of about 1/20 at f/3.5 to take a stable shot.
The higher the shutter speed at a particular lighting, the wider the aperture must be to keep a constant exposure. Eventually you will hit the limitations of your aperture, and you will need additional lighting to keep the shot bright enough.
If you are taking shots at night or indoors, try using your flash. Even in lit conditions like indoor sports, a flash can help brighten up a scene and freeze motion.
As a final resort, you can increase your sensors ISO setting. Automatic modes tend to change the ISO as needed to accommodate lighting conditions. Once you start using semi-automatic and manual modes, however, you may need to adjust ISO manually as well. Some cameras also limit the maximum ISO that may be selected automatically, which is usually about ISO 400, possibly ISO 800. If you need to use a higher ISO setting, you will likely need to choose it manually even in a semi-automatic camera mode.
A high ISO setting will allow you to use a faster shutter speed in lower light. Where you may only be able to use a shutter speed of 1/20th of a second at ISO 100, you could use a shutter speed of 1/160th of a second at ISO 800.
If you can't improve your shots by adjusting the aperture and shutter, or by using flash, you might want to get a tripod. Attaching your camera to a tripod greatly improves the stability of your shots over hand-held.
You might also try using a semi-automatic camera mode rather than full manual. Most cameras support aperture priority, shutter priority, and program modes. Aperture priority allows you to choose the aperture, and it will automatically set the shutter speed for you. This is probably the most common camera mode used by most amateurs and professionals alike. If you need control over motion, shutter priority is probably better, as it will allow you to choose a shutter speed and automatically set the aperture for you. Flash in combination with shutter speed will give you more control over freezing motion. Program mode is a mostly automatic mode that usually provides some control over exposure compensation. You can expose at zero compensation, or compensate +/- 1-2 stops (perhaps more), and the camera will automatically set shutter and aperture for you, accommodating your compensation.