I'm assuming you're starting out as fully human. Baseline Steele.
Go full nyrea with the rock candy found on Myrrelion, then go back to Tavros and savescum dracoguard until you only get a gryvain tail. While you're there, visit the salon and remove all your hair. Pick up a zil ration on M'henga and savescum that until you only get the long and hollow tongue, should be very close to the whole "inner mouth" thing. While you're there get some kerokoras venom and savescum that until you get the ears and digitigrade frog legs. That's the only way to get digitigrade legs that I know of that doesn't include fur or becoming tauric in the TF. Use others in a similar fashion if there are. Then go to Uveto to pick up a pickmentation and use the metallic option's onyx colour to change skin colour into something like a xenomorph's while keeping the nyrean chitin plates. If you really want to you can go with shark bytes or another predatory tf and savescum that until you only get the face that has in its description something about sharp teeth.
Depending on how close to the classic depictions of xenomorphs you want your pc to be you can either keep their current tone and thickness, or for a more authentic look you can drop the thickness down to 24(thin body) in the gym and up the tone to 51(defined muscles). You can also mess around with genitals and breasts as much as you want. I've seen art for big and small tits and xenomorph cocks like human, horse, and even ovipositor ones. Since going full nyrean in the beginning gets you an ovipositor one I recommend sticking with that. If you're going for a xeno queen vibe I recommend making your character really tall and having one of the butt bug parasites to facilitate at least semi-continuous egg-laying. That or a cuntsnake, but you'll lose out on the tail gained through dracoguard which is to my knowledge the closest part to a xeno tail.
I may have missed something obvious but that's more or less what I did once a good while back for a phaux xenomorph character.