I understand the theory behind learning to fold a model from a crease pattern, but given that CPs are more a tool for designers than folders, there doesn't seem to be much intermediate ground between trivial "here, do a bird base..." lessons or "just do it" basic advice; and people posting triumphs about solving some super-complex Kamiya CP. But given that some of the more prolific and complex designers don't have the time/energy to spend on diagrams for many of their models, but are still willing to publish a CP, this is a skill I'd like to master.
But in the learning resources I've found, it's all frustratingly lacking in hard advice or practice pieces in the middle.
What do I need to look for in a CP to judge its difficulty level? I don't want to get so frustrated that I give up all together, but neither do I want it to be so trivial as to be boring. Is it just how dark the grey value of the printed CP is? :) Is there a good learning resource for bridging this middle ground to CP mastery?