1. Balance the light.
Uneven lights and shadows can make a good photo look "unfinished" and distract the eye from the actual subject and meaning. I almost always balance my picture using shadows at the edges and the majority of the light on and around the main focus of the image, often close to the middle, surrounded by the darker shadows. I do all this in a subtle way, but sometimes I take it to the extreme for dramatic moody pictures.
Either ADD some saturation or REMOVE some saturation, depending on what kind of mood you want to create. Less saturation gives more of a vintage feel, and a subtle rise in saturation can bring life and spice into any image. Often after doing this you need to lower the RED's saturation in the skin tones. You do this the quickest by adding a layer mask. To rich red on human skin will only look like sun burn. Focus the saturation on different part of the pictures instead. Something else that can be effective is to put most of the saturation on ONE color or even all the cold tones.
3. Eye boost.
Bring out the eyes by brushing on some subtle saturation and light, as well as darken the pupils and the shape of the entire eye. If the model is a woman you can also darken her eye makeup.
3. Clone tool.
Use the clone tool to remove unwanted details, especially useful in outdoor scenes and landscape photos. Remove distracting elements one by one and your picture will get a much cleaner and more balanced appearance. You can also clone away stray hairs, overblown highlights and too dark areas.
4. Subtle skin adjustments.
The key to retouching skin is to keep is subtle. Use the healing brush for uneven spots and add a low Gaussian blur to ONLY the skin. Mask out eyes, lips and dark edges such as nostrils and the curve of the chin.
5. Color correction
Use "color balance" to add or remove tones from your photo. You can choose to only apply this to either midtones, highlights or shadows, or to apply it to the whole picture. After doing this, go to image-adjustments-selective color and treat every color, one by one.
6. Blend modes.
Double your layer, put it on either soft light or overlay. Optional now is to add a slight blur to it. Lower the opacity if the effect is too strong. These blend modes both deepen color and add contrast to your picture, making it richer and more attractive. You can even try multiple ones. If you need your image to be brighter, try screen. If you need it to be darker, try multiply.
7. Add warmth or cold
This step is very optional but can bring out a lot in photography. A very simple way to do this is to go to image-adjusments-photo filters. You can then choose between both warm and cold tones to add to your image, as well as custom picking your own colors. Sometimes picking more than one option will give a more interesting effect, you simply pick one filter, click ok, then merge. Then you double, open the box again and choose a different filter.
You always sharpen as a LAST step. Also remember that resizing the entire image or parts of it is likely to blur it a little. Just like with everything in photoshop you can control where you want a treatment applied by using layer masks.
Once you get a good work flow going, it will go very quick and be very easy to make your beautiful pictures look even better!