a- It’s what I call tidying up the model.
It’s fixing the model’s body from her waist. I also always love to make her a bit taller and her dress with more volume using the liquify filter (Filter>>liquify). I made a video tutorial about it you can view it here. You can also find some useful tips for manipulations here.
b- I choose where the main light is coming from (usually either left or right).
Keep that in mind for the whole process of the photo manipulation or maybe add a note on a single layer.
c- Cut the model out. My favorite tool is the pen because you can go back and readjust the selection even after you’re done with it. Here’s a tutorial on making selections using the pen tool. It’s ok if you’re more flexible using another way of cutting, but I recommend the use of masks.
d- Dodging and burning or what I call it shadows and highlights. This is related to the mainlight we made in step “b”.
For beginners I see it hard to use the most known way of it. I made a simple way and I always use it. Here’s how to do it:
Create a new layer (Ctrl+shift+N)
Select your brush tool (or press B). Hardness should be 0% and sizes depend on the area you’re working on with opacity 30% and Flow 20%.
Tip: To be faster play with the brush size with “[“ and “]” and the hardness with “shift+[“ and “shift+]“
Use black to make the shadows and white for the highlights. Set the layer blending mode to soft light.
To make some areas pop-out more (like the cheeks, hair, etc…) make another blank layer, use a white brush and set the blending mode of the layer to overlay.
You can always play with opacity and fill to get your desired result.
If you want to add makeup. Create a new layer, also using a soft brush with low opacity and flow then choose the colors you want. For example light pink for the cheeks and red for the lips.
f- If you are a beginner and don’t have a tablet, I suggest using hair brushes. There are multiple high quality hair brushes on deviantart. Here are some links: link 1, link 2, link 3. To use the same color of the model’s hair simply use the eyedropper to clone the color of the hair then go back to your brush and place it on a single layer so you can modify it, transform, rotate, etc…
Feel free to ask further questions.