Oh wow, thank you so much for starters :D
Making visual novels is incredibly exciting and such a sense of accomplishment when they're done, I'm so glad you're deciding to give it a go!
My advice would mostly be to be organised and keep the length manageable. Also, try breaking everything into chunks or chapters, I find it much easier to work through smaller chapters, than try to blow through the whole thing in one go. Finishing a chapter gives you sense of accomplishment, and that you're moving forward, where as slogging through the whole thing in one go can feel a bit much at times.
Also, if you're really stuck on something, just move on. Move on to something you know you can finish, then come back to that thing later with fresh eyes and a fresh mind :)
And most of all- enjoy it! :D
I wish you the best of luck with your project! It really is worth it :)