Advertising is a hard one, can't say I master it yet. But coming from a guy who rarely did it to one that is starting to figure it out, I recommend to really understand out what is the most important part in your game. What's the "Wow!" factor, the hook. Most of the times is easy to overlook as you already know the game in and out. But figuring out the thing to get people excited before even playing is the key for making a sale.