If you have not already done so, I would start simpler than the Loomis books. Basic geometric shapes. Draw and shade spheres, cubes and cylanders. Everything is made up of geometric shapes, and it is easier to start with the basics, then move to more complex items, like still life's of flowers and things, then go large, and do things like buildings, cars and street scenes and then move on to people. And always use a refrence. Something right in front of you is best, but a photo is better than nothing.
Start small with the basics (anatomy, value, perspective and shapes.) Draw everyday even if it's just a doodle and watch what you're doing. Take as long as you need to to get it right and refrence is okay dispite of what some people will tell you.