Some tips for sharper images

"Get it right in camera"

The old mantra "get it right in camera" applies here, as only very slightly soft images can be saved by sharpening in post processing.

Handheld or tripod?

If there is lots of light and you are working with wide aperture settings you can probably work handheld, however for longer exposures and/or low light conditions some kind of stabilisation is often required.

Working handheld

If shooting handheld the metric for estimating if the image will be sharp (no shake) is ... 1/[the lens mm]. So for a 50mm lens shots at most 1/50th of a second should be sharp and for a 400mm 1/400 of a second exposure is needed to get things sharp (at longest). The lens magnification factor amplifies any shake.

Stabilise the camera

Use a tripod. If it's windy and there's no chance of lens flare, remove the hood to reduce buffeting. Weigh the tripod down with your camera bag (some tripods come with a hook under the central column for this purpose).
For best stability extend the tripod legs as much as needed and avoid using the central column of the tripod.
No tripod? Brace yourself against a tree or a wall or another available surface.
Squeeze the button gently
Stabilise yourself, and breathe slowly when pressing the button
Use the self timer or a shutter release for longer exposures (wireless and tethered cable devices available)
Use mirror lockup (more for very long exposures)
Budget permitting, use a lens with image stabilisation (Canon: IS, Nikon: VR) (Note: If using a tripod, turn off lens image stabilization as it will attempt to correct non existent shake and introduce a little shake!)

Bump up the ISO

If you need a faster shutter speed, bump up the ISO.

Do also consider the noise trade off. This is improving as camera technology advances.

Focus point

Focus on the eyes - even if nothing else if sharp, the eyes should be sharp
For landscape shots with lots of detail choose a small aperture and focus about 1/3rd of the distance into the scene to get as much as possible sharp

The "sweet spot" for a particular lens

Each lens has a "sweet spot" or optimal aperture at which it operates. It's around 1 - 2 stops above the widest aperture. If you want the sharpest pics your lens can produce, shoot at a stop above the maximum, i.e if the max aperature is f/5.6, the lens will be sharpest at f/8.

Subject in motion

If the subject is moving (e.g. flowers blowing in the wind, bird in flight) a faster shutter speed may be needed to freeze the action.
Rear curtain flash is a nice way to freeze some detail while keeping some movement.

Sharpen with Unsharp Mask

All digitial images need some sharpening in post processing. Many people sharpen at the end, after completing any other post processing as this is a good way to prevent introducing artifacts. "Unsharp Mask" is generally regarded as the best sharpening tool.

Unsharp mask parameters:
Amount: The amount of contrast added at the edges.
Radius: Size of edges to be enhanced. A small radius enhances small scale detail. A large radius can introduce haloing.
Threshold: How different neighbouring pixesl need to be before sharpening is applied. At 0 all is sharpened. At a higher setting similar areas will not be sharpened.

Some sample settings for sharpening with unsharp mask:

Sharpen for web - Amount: 50-100%, radius: 0.6, threshold: 1
Sharpen for print - Amount: 150-200%, radius: 1, threshold: 2

How to get pin sharp images