I'll be easy to please because I just want new footage of Predator(s) hunting and killing humans.
Bonus points:
Having the story relate to Dutch and his team, possibly Arnold's cameo where we see Dutch is obsessed with Predators, has a bunch of news articles cut out and is analyzing any UFO reports, stuff like that. It wouldn't be wise to have Dutch deal with a Predator in person again, he proved himself already, I'd say Predators respect him.
Have the Predator survive at the end. We're Predator fans, not Team Human fans.
Reveal some new things about them, as they probably will as Shane said there's a lot to mine in the mythology, but don't reveal too much. A lot of Predator's epicness is in the mystery around them. Having scenes like them going about their business on their home planet might ruin it, unless that business is all about the hunt. It's hard to imagine how they sit down and talk about new strategies or weapons designs like they're business men, but something like that is going on if we can assume they created their technology. We don't need to see that, let them remain a mystery for the most part, but do reveal new things concerning ther ethics, way of thinking, why they hunt, etc. In short, reveal more about the badass stuff, hold mystery the other stuff.
If it's a prequel, connect it to the original, for example having the original Predator there somewhere even though it's set 200 years before.
Predator movies are not easy to do because you can't make a story about an alien hunter killing humans many times before you're out of ideas. So the story should be something bigger than that.
But as I've said, I just love seeing Predators on screen doing what they do. I doubt any new Predator movie can ever top the original, but I have a feeling this new one will be a step into the right direction and something the fans will enjoy.