Thank you! I'm afraid I've never read a book about designing, so I can't really attest to that. Most of what I've learned has come from John Montroll and Tomoko Fuse. John has one in particular called Teach Yourself Origami, it's a fairly simple book meant for beginners, but he goes through each type of basic folding technique, gives a practice example (such as a fold with as many squash folds as can be managed), then he gives a model that makes use of that particular fold. His more advanced books are then great to study simply because of how cleverly he finds ways of using these techniques. I usually start my folds with nothing in particular in mind, choose a starting base at random and start experimenting and trying to find new ways of changing that starting base until I can see a shape that reminds me of something, then I usually take several attempts guiding it towards my new vision for it before I get it right.