I suppose my best advice is to not ignore the importance of your audio. Your phone is probably a decent camera already, so with a bit of set dressing and lighting, you probably already have what you need for good video – but good audio is tougher to do DIY-style.
A blue yeti is a worthwhile investment (same mic Jeremy uses and they’re about $100-150 depending on what kind of deal you can find), and watching some YouTube videos about how to clean up your audio with Audacity (a free audio program which is awesome), is a very good way to prepare.
Finally, high quality gameplay footage is a must and there are many ways to achieve it, but whatever method you use, go into the settings of your recording software and crank things up as high as they can get. Make sure things are capturing at 60fps, or some gameplay will look choppier on playback than it should