First you want to start with the best selection possible. Here you have some choices.
- Select using lasso, quick select (not ideal unless you want to do lots of adjusting). If you do use these, once you've made the best selection you can, click on the Refine Edge button in the tool bar and use the sliders to inteligently adjust your selection.
Near the bottom you'll see Decontaminate Colors. This will remove some of the blue sheen that may be on the edge of the subject from the background sky. This refinement will do a pretty good job on solid edges and a fair job on hair.
- In many cases, a better alternative to manual selection like the lasso tool is to use Select > Color Range (below I clicked in the blue sky and selected invert - a couple of clicks, done)
After making your selection, I would use it to create a mask. Then refine the mask. Using a mask means you don't delete pixels from your original, so it's non-destructive. Again, several choices:
In the masks panel, select Mask Edge. This will give you some sliders to work with. I'd suggest selecing "Smart Radius" and increase the radius to a few pixels. This is the same tool as Refine Edge from above, that you may have used along with the quick select.
Or go into quick mask (shortcut is "Q" key) and then you can use a soft white or black soft brush to tidy up areas. I wouldn't do pixel by pixel, just use a small soft brush very carefully.
You could also get a good mask by the following steps:
- Create a blank (white) mask, and click to select it
- Image > Apply Image
- In the source channel, select the blue channel.
- Click OK. This will use the blue channel as a mask. Since the sky is blue, the sky areas will be very light, and the subject will be darker. Invert that mask to get a good starting point. You can then use levels to adjust the mask to higher contrast (b&w rather than various shades of grey). This technique is similar to select color range. Good for selecting skies for replacing. Or you can use the red channel to select skin for retouching portraits.