Colouring books for adults.

I will do thanks.

Try YouTube for art lessons. Some of them are excellent.

Thanks both of you for your advice.

I love the books by Johanna Basford. It feels like she puts a lot of thought into them.
www.johannabasford.com/
Some of the pictures that people create from her line drawings are amazing.

If you want to develop an art skill then it won't be a colouring book you need..though think they can be satisfyingly calming.
Have a look out for online tutorials or art sessions..they may give you clearer guidance on the particular aspect you want to learn.
I am not particularly artistic..Dick Bruna is my style