I started a new writing project about 4 months ago. I thought - about a year ago - that I knew what my next project would be - an historical fiction piece based on the lives of my grandparents. While I know I will get around to writing that one - some day - the one where the energy is, writing about the village I grew up in, has raised its head and has all the energy at this time.
Someone recently asked me if I get writers' block. I have to answer "no" but I do have topics and projects that just don't have enough energy for me to concentrate on them at this time. I encourage my writing students to find the topic/subject that has that energy - that piece that calls to be written at this time. Then write.
First there is the period of research, collecting topics, writing vignettes that every project requires. Then I need concentrated time in which I am not distracted so that I can distil all the information into a coherent whole - a story. Then I have to start to write in earnest - mapping out a time line for the characters, writing character sketches so that I know what is within the realm of possible decisions, emotions, actions of each character, thinking about the main struggle or conflict and how that will emerge.
All this takes time and energy - and each project is different in its emotional pull and challenge. That is all part of the fascination of writing. So, it may not follow that if you have written one book the next will be easier.