It might help to try posting something original here instead.
I don't like trying to critique something I can't easily tell how much of it is *your* work because it's difficult to know what *you* did right and what you did wrong vs. what the original artist did right/wrong, therefore making it difficult to offer you any advice at all.
Just something to think about. Try shading a vase or statue or *anything* that's not based on someone else's work / construction lines / shading / etc.
You will get a lot more feedback by making it clear to us what you're capable of currently so that we can help you grow from there.
You're obviously not at this level yet (or you wouldn't be asking questions on how to shade stuff), so try posting the best pixel work you can do completely on your own so that we can help you increase your skill level by offering advice on the things we can see you need help on.
"Teach me how to shade" is more something you'd look up tutorials on than ask about in a forum. On the other hand, if you've read that stuff and still don't get it, you should instead show us what you know via an original example and ask "What do you see wrong with this image that I'm missing and how can I fix it??"
The image you've provided currently doesn't tell us your skill level at all -- it just emphasizes that you kinda wanna know, but aren't really interested in doing your own stuff to actually learn (which also inadvertently tends to turn many skilled people off from wanting to spend their time to help you learn, which is unfortunate if you really do want to spend that time to learn -- and also why I'm posting to your topic to inform you just in case).