Get loomis books
http://alexhays.com/loomis/
Also Bridgman's and Vilppu are awesome.
Also, you can't learn to draw if you don't use references, like Picasso said "To copy others is necessary, but to copy oneself is pathetic". You can't draw something if you don't know what it looks like, to draw from imagination requires a big deal of practice, what is called a "mental library" among artists, which includes everything you have ever seen and analyzed, and your muscle memory. I don't recommend you learn from manga style, draw manga if you want, but when doing studies draw realism, and then learn to apply that to your preferred style.
Here's two must-read threads in CA:
here and
Here.
Also, drawing the figure is one of the hardest things in art, at least for realism, it is a process that takes years. Never be afraid to practice the basics, draw and render boxes, spheres, cylinders. Every object in the world is made of these simple shapes, Vilppu and Bridgman have really me helped see that and allowed me to improve a good deal on my studies, so I recommend their stuff.
But most important above all:
Stop worrying, stop coming up with excuses, and just draw, draw and draw.