Building out your product's first features

So my team and I have been hard at work to finish developing our app product, and as the visionary and product designer and director, I'm beginning to make a list of features that will be added within the first couple of months of us launching. My question is: how have you guys chose what are the top new features that will be prioritized and built? What are some best practices for first new features of a software product? Any advice would be appreciated!