So, now that summer is soon gone, I will probably come back to working on some of my manga projects. That's why I wanted to practice a little with greyscale beforehand. The lines are not mine, since I realy wanted to focus on the greyscale part.
Finding how to do just enough (not too much, not too little) is quite hard, I must say. I used multiple manga pages as reference for this. What I found out is that you need to do as little shadows as possible, in order to prevent taking too much time. Some mangas have very detailed shadows, but I think this is because the drawer has a team to help him out. Most mangas don't even have shadows, some even using only white and black.
I settled for white, black, and two nuances of grey, plus one for shadows in white spaces. I putted shadows in as little places as possible, focusing on the neck, and the parts where there would be intense, cut shadows, like under the sleeves, in the ears, or under the chest. I'm probably going to only put shadows on these areas in the future, unless when I want to greatly emphasize on the shadows, like when there is a dim light or for drama.
I also made gradiants when I felt like it would be okay, mostly on the hair, and a little on the horns (they feel more "organic" this way). From what I saw, I feel like gradiant shadows are much of a "feeling" than a "real rule". Putting too much progressive shadows makes the image heavy, and needs more work. It can make the drawing more realist, but it is not needed. But it still could be of great use for dramatic settings.
Also, not every manga does this, but I find drawings lines in white in black areas help reading the drawing a lot, especially if your manga is really dark. For the leather/iron effect, using thin solid white light also helps making the drawing more readable.

What do you think about my observations ? Do you have other tips ?
Also, if you were to start a manga or if you already are doing one, what would you mainly practice on beforehand ?

Original : http://magnaleon.deviantart.com/art/Succubus-LineArt-259275069

Line©MagnaLeon
Greyscale©Rachel/Almarane