An excuse that sometimes comes up for not writing is that you have so many ideas and you can't decide which one to write.
First, congratulations on having a lot of ideas!
There are two main criteria for deciding which idea to work on. One is how excited you are by it. Writing a novel or screenplay takes time and effort, so the more excited you are by the project, the more likely that you’ll stick with it.
I’m assuming you’d like to sell your book or script, which is where the second criterion comes in: how much of a market is there for the project? While you can never be sure, you may be able to make an educated guess. The main question to consider is whether you have a fresh angle on a popular genre. If so, you may be onto a winner.
A good strategy is to assess each of your ideas using these two measures and choose the one that scores highest in both. Then commit to it and don’t second-guess your choice when the going gets tough.
Sometimes people say, “All my ideas are equally good, I just can’t choose between them!” This excuse is just a humble brag that makes procrastination sound like it’s the result of genius.
If you think all your ideas are equally good, flip a coin. Choose one, start and finish it, and move on to the next one.