As a short-timer to book writing, I'm amazed at how many people I've already met that aspire to write a book, but just haven't started. The task can be daunting for sure, but the reward of seeing your finished product is well worth it. One thing I've found, having one published book and one in initial draft, is that it's much easier to get started when you write about something you love.
When I started writing the Bruten & Tommy series, I followed my life experiences. I've always loved to help put on events for kids in my neighborhood, and I'm always one of the guys who jumps in to play games with the kids at gatherings. In fact, my friends and family will tell you that I'm just a big kid at heart (sometimes to a fault). I like nothing more than taking the kids on an "adventure" to a new place or looking for treasure (geocaching). It was not hard to make the leap to writing an adventure book series for kids.
This will probably seem strange, but with both books, I had the same feeling as I wrote the last part of the book. It was as if I was reading it for the first time, and I really wanted to see how it ended. On Secret of the Portals, I literally wrote 10,000 words in two days. On the new, yet to be published book, Guardians of the Scepter, I wrote 9,000 words in one day! I just had to get to the end... not because I was tired of writing, but because I was excited to see how it would end and where it would lead for the next book. That feeling of reading the book for the first time can only be explained by the fact that I love what I'm writing about.
When you decide it's time to write your first book follow your life experiences and your passions, and take the time to find something that excites you when you write about it. Find a topic that you can't wait to talk about. It will make things much easier to go from wanting to write a book to actually writing one.