Prequels pretty much killed the franchise. But when done right, it's still possible to get back on track.
There's only couple basic guidelines that need to be followed (although some of them can be very hard to pull off, but anything less won't do)
-Soft reboot set in original universe
-ignore prequels or spin-offs (completely, as if they don't exist)
-strong retrofuturistic aesthetics, that means no fancy holograms a la Minority report, but don't go overboard with the retro stuff (no need for analog tapes etc)
-use cgi only when absolutely necessary. Environments can certainly be computer generated with today's tech but cartoony character cgi a la The Thing preguel, Alien Covenant... will ruin it. Camera needs to be/seem real, no Marvel style motion trickery/camera floating all over the place. All in all, less is more.
-creepy uneasy uncanny and timeless soundtrack. Avoid the cheese, there is no place for tacky music in Alien universe. Doesn't mean it can't be adventurous or beautiful in places. But music must be as strong as it's visuals, otherwise it wont work.
-realistic cast and characters (really important)
-no new stronger super duper Aliens, you can't outdo what Giger created with the beast design wise. But perhaps expand it's behavioral traits to emphasize it's otherworldliness. Don't make it a dumb animal jumping around with aggressive rabies that will get killed in stupidest of ways.
-minimalist storytelling that is full of smart and subtle detail. No need to spell everything out to the audience.
-don't link aliens with human history to fuel our ego or for some other misguided reason. AvP did it first and failed, Prometheus and Covenant has made the franchise almost beyond repair. Alien needs to be alien. Also don't set the movie on earth, at least for the next couple of movies. Space makes the alien presence much more effective.
-need I emphasize that the atmosphere must be nailed. In rare cases it can redeem a mediocre script (Alien 3)
-most importantly, green light the production only when there is a truly worthy script. Don't do it because you have a franchise sitting in a box waiting to get milked.
Basically study why the original films are so powerful, why the prequels are not and go from there. Also take some notes from the better aspects of Alien Isolation.
