I've always wanted to write a space themed book and why not do it Harry Potter style? By Harry Potter style I mean 80% of the book focuses on finding and colonizing planets and said planets visual views while the other 20% is a sub plot that is slowly builded up.
Background: This book takes place just after Earth becomes unhabitable after climate change but we were smart and colonized Mars and the Moon. Since the Sun is due to explode soon (in 500 years) humans and probes are sent to explore our galactic neighborhood. And of course a smarter alien civilization sees the humans and starts preparing for the worst but this is only hinted at until the end.
I'll let you think of some characters
Don't forget to have inmportant info like the time zones, rotational speeds, etc. I recommend writing all the data about the planets down somewhere so that everything is accurate and makes sense.