not NN, but had the same problems, I just offer for reference and want to have any comments.

having looked up tips of NN from CD, I think the these materials are very important to master the essentials and cracking skills of CR, such as, OG, FeiFei CR, and CR Daquan. they are musts. OG helps understand the meaning and rules of CR, understanding of content is more important when work on OG, I use other two materails to practise speed.

btw, if time allowed, the more materials you study and master, the higer and better you will score in test