As Adrian said, it’s all about the practice. I think what I only have to add is the Pothead course, it’s such a complete one:
https://cgcookie.com/courses/pothead-create-a-hard-surface-character-in-blender
And never underestimated the classics, old courses have so much timeless knowledge in them, even though the Blender UI might look different, it is of little consequence:
https://cgcookie.com/courses/modeling-a-sci-fi-helmet-in-blender
https://cgcookie.com/courses/introduction-to-hard-surface-modeling
https://cgcookie.com/courses/game-character-modeling-with-blender
Same goes for the Modeling Bootcamp, it’s filled with gold:
https://cgcookie.com/courses/blender-mesh-modeling-bootcamp
