Try restricting yourself to only 2 or 3 decisions that will affect the story line. It's important to understand the development cost of each decision - doubling the size of the project vs adding a short scene that'll influence a later scene (or even not do anything other than be a part of the experience).
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That's great advice too! What I've decided to do for my first project is fairly simply. i would love to do a branching path, but I think I'll do optional questions. Add in some some things that have more lore. The player isn't required to do them, but it'll be there if players explore.
I just get excited thinking about the different possibilities and ideas.