I found the book The Magic of Spice Blends immensely useful in learning more about the world of spices; particularly surrounding the history, culture, and culinary uses of each of the 50+ spice blends included. If you enjoy cooking from different cuisines then having this book on hand would be extremely valuable. Since you're selecting different quantities and (almost always) toasting the spices before grinding, you really get a better understanding of each flavour profile. There's also recipes included to get use of the spice blend you've made.
Take for example, I always found each store-bought harissa paste I'd buy could taste dramatically different from each other. And there were certain ones I LOVED and certain ones I found to be meh. Once I made it completely from scratch as per the recipe in the book, it really opened my eyes as to which ingredients are important (to my taste). I found that using the suggested smoked paprika instead of sweet paprika, and lesser quantities of red chilli for heat was more ideal for me.