It's an enduring challenge to visual artists to create the impression of 3 dimensional objects on a 2 dimensional surface, the picture plane. The ancient Romans had the knack of perspective and employed it in their wall friezes; I saw some preserved at Herculaneum, Naples. I believe perspective techniques were forgotten during the dark ages and rediscovered by the Renaissance artists, and we've got lots of aids and techniques to help now, but in the end, it's down to careful observation and lots of practice.
Working through a series of OCA exercises on texture and form, I’d forgotten the simple effectiveness of creating visual textures by rubbing graphite over paper resting on a textured surface… it’s called ‘frottage’, though it turns out the word has more than one meaning… A bit of a ‘Carry on Camping’ moment!
Still life is another exercise that can feel rather repetitive, perhaps dull, but it’s a great way to practice observational and drawing skills. It helps to develop composition and form, texture and tone, as well as helping us to see the beauty in the everyday: consider the still life works of Dürer, Chardin, Cezanne or Braque. I've collected some of their amazing work on my Pinterest board: https://uk.pinterest.com/elliottreed/still-life/
And for the OCA exercises, here are some of my recent still life sketches, hardly Cezanne! But I'll keep trying...
And here's a great little video on YouTube that shows some still-life techniques: