If you don’t have basic drawing skills, you might want to start off with something easier to build up your eye-to-hand coordination and observation/analysis skills. Maybe some simpler images like cartoon drawings, comic book illustrations, etc.
I highly recommend you get Andrew Loomis’s Fun With A Pencil. It’s a classic art instruction book that starts off with beginner lessons and then gradually work up towards intermediate stuff. After that, Successful Drawing and Figure Drawing For All It’s Worth are two of his most famous books and legendary among artists. Creative Illustration and Eye of the Painter are also very good, though not as many people know it.
When you choose references to practice from, you have to know what type of references are the most effective in training specific skills. If you don’t choose the right images, you could so a bunch of them and not learn the same amount as you would if you picked just one really effective photo that really challenges you in all areas. This is where an experienced mentor can make all the difference, as he would know exactly what you need to work on and how to best train specific skills, thus saving you years of wasted time floundering on your own and now knowing how to learn/train effectively.
