Sharpen & soften
An advantage over conventional photography is that in your digital darkroom there are several possibilities of applying filters to enhance an image.
Probably the most useful is Unsharp Mask as many images captured with a digicam will benefit from some level of sharpening. This filter enhances visibility of boundaries between light and dark tones in an image. You can adjust several parameters (Threshold; Amount and Radius) to fine tune it to your exact needs.
A useful filter to make edges or borders in an image less prominent is Softening or Blur. Female portraits or romantic subjects will be more appealing if they are a bit soft.
Sometimes it will be necessary to sharpen some parts of an image while other areas will benefit from softening. You could do this by making two duplicate layers of your image, sharpen the top one and blur the other. By using the eraser tool on selected areas of your top layer you can erase the sharpened parts that need to be soft. If you apply a feathered eraser, edges will not be noticeable. Also the soft filter might be handy to blur an intrusive background. Loosely select your subject with a feathered lasso. Reverse the selection and soften the background by applying Gaussian Blur or any of the many other blur filters.