I like Bert Dobson’s book Keys to Drawing. He talks about inner dialog while drawing which is very helpful.
Regular practice drawing from life really pushes you skills. I used to sketch my fellow commuters every day on the train.
I find life drawing really helps. You brain is so attuned to what a human looks like, that it will be obvious where you have gone wrong in your drawing. For practicing to draw what I see, I draw in pencil and sight sized.
You could try joining an Urban Sketchers outing. It helped me get more comfortable sketching in public.