However, the big motivation problem for me is getting motivated to actually write. I mean what good does it do to have the ideas - sometimes even knowing where an entire book is going - only to never write. Now that there is one book out, it only makes sense to complete the second that is underway, so I can say I have a series.
A confession - I have, and have had, a third of the follow up book done. For a while.
Sure, I have family, work, life distractions, but all of the outside forces competing for my time were present when I wrote the first book and I got that done.
So how do you, or I, get past it? (At least these are the things I did before that worked.)
First, make yourself write. If you don't get something down on the page, even pure crap, you won't have anything at all to work with.
Second, make time to write. In the past I have scheduled a specific time. Recently I went back through and edited my second book, or at least the progress so far, and set a time early each morning to do this. I'm going to continue to do this with the writing.
Third, set goals. I try to write a certain number of pages each day. Some people will have completion dates. Others a scaled in schedule. Use whatever works for you. I once saw a John Grisham interview where he stated the proposition that to be a writer you should write a page a day. That is literally only 30 lines of type a day. Just a few hundred words. However, if you can do this, that is a book a year. Not bad.
Reward yourself as you complete chapters or even a critical scene.
The point of all of this is writing while fun, is also hard work. Even when you are writing fiction. However, if you just put pen to paper your are literally halfway there. Now to just make myself do the same thing....