I resize them to 1280×720, use smart sharpen, add a brightness/contrast layer (increasing brightness by about 30, depending on the screenshot and contrast by 5) and a hue/saturation layer (+20 to saturation). On the top, I add a white to black gradient layer set to Soft Light at 75% for a nice vignette effect.

I use an action for 99% of this, so it’s a lot quicker than it sounds. Hope that helps 🙂

EDIT: I forgot the screen layer! Before I sharpen them, I duplicate the screenshot and set it to Screen at 50% opacity for extra brightness.