Just about every app I've worked on has required an interaction concept that involved typing. When you have the time to simulate real typing, it can go a long way toward selling that realism we're all going for. This is how you do it.
A walkthrough or intro is the first place you get to delight your customer, why make them slog through boring static screens? We'll add some life to this intro screen and tell a (very) short story in the process.
Layout grids can help you achieve a modern version of pixel perfection in your designs. It's easy to be loose and fast with Sketch, but using layout grids will ensure no surprises when it comes time to animate or develop your designs.
If you're not already using shared styles and text styles, you should probably start now. It's a huge time saver and helps avoid inconsistencies in the long run. This video shows how they work in Sketch.