With a whopping two under my belt now, I already see a pattern. These are slice-of-life tales. The main character in each book is a pre-teen girl learning to navigate the world around her, by understanding her family, making make friends, and grappling with the bigger pictures of life.
The two stories also involve mysteries. In Manifest, Abilene wants to learn about her father's childhood while in Reach Me the quest is to learn the identity of whoever is leaving secret notes. Manifest and Reach both engaged me in the overall stories and characters. However, the former did a little too much signposting and left me feeling a little letdown by the finale. The latter had peppered in the clues so that it all came together in the end, but I was still scratching my head a bit.
I have integrated some mysteries in my own endeavors writing Otter and Arthur and the Sword in the Stone and now fine-tuning its sequel, Otter and Arthur and the Round Table. The lesson is to make sure the reader will 1) want to learn the outcome and that 2) the reader will be satisfied with the outcome once it arrives. This means that the reader must be well-invested in the characters and the story, but also that the ending comes across neither as too signposted nor as too much of a surprise.