I actually had a whole story planned out for AVP2 that I posted in another topic a while back, but I can't be bothered repeating it here, lol, so I'm just gonna note some of the basic stuff that I'd do.
-The Predators & aliens would be taken back to their roots, the classical designs, with a few new styles of course, but for the most part, their basic style would be similar to the originals. This time around they would actually act like aliens & preds, we wouldn't be seeing rubbish about thick-headed preds blindly rushing into battle like some kind of gladiator, nor would the aliens be acting like raptors, they would be very much akin to their classic counterparts, along with the classic sound effects, as most fans would know that nothing truly completes the alien & predator style quite like the traditional sounds of the creatures & the classic music.
-Fear, something that hasn't been conveyed in a pred or alien movie for a very long time. The movie would be very dark & creepy for the most part. It wouldn't all be doom & gloom of course, as there would have to be big action moments between the 2 creatures that would have the audience cheering for their favourite side, but in most instances when the humans are involved, the movie would take on a much more creepy tone, with startling moments that would make audiences jump out of their seats.
These are just a couple of quick examples, but I hope u get the idea of what I mean