Before marketing a gaming app, what should I do about IP?

Protectable features of your gaming app may include the artwork and source code (under copyright), the name of the game (under trademark), and perhaps any sufficiently new, useful, and non-obvious inventive function of the game and its interactions with the user / computer networks (under patent). Contacting an IP attorney to help identify what assets you may protect, and how best to do so, is your first step.