I end up playing aliens quite a lot, many times I will play as the Queen. I love strategy games, especially city builders. So to no surprise my tastes and experiences reflect in my style of game-play. I love to build a big badass defensible hive like it is some kind of Dungeon Keeper game. Usually if the marines win it is in the early or mid stages of a round, as when a round is longer in play that usually coincides with the aliens attempting to uproot the marines from their big metal bird, thus the hive is irrelevant at that point. Certainly marines can still win at this last stand stage of the game, but what is a pivotal time frame for most rounds is that early to mid game transition phase when the aliens start trying to leave their hive and expand into the colony. (Having exhausted all the furry hosts, this becomes necessary to capture more hosts... if they aren't coming to you already that is).
So like the marine's own last stand situation on the Sulaco, the aliens essentially start off playing hide and go seek with the marines struggling to survive any large (and usually uncoordinated) attacks on their hive. Marines may establish the table fort and if they get a strong enough foothold this is where the meatiest game play takes place in my mind. The battle of Waterloo if you will. The marines are on the prime of their offensive and the aliens eagerly await their advances (usually) from the caves.
However a picture referencing my work in fortifying my hive as the hive lord for the round shows our hive to be centered out of the crashed shuttle. Which gives me the perfect grounds to explain my strategy since it is surrounded by open fields excluding the strange temple containing caves just to the east. (Which won't be pictured but I'll have you know I also fortified the duck out of, I say this because as I stated earlier, hive lord 134 did not survive til' end of this guide and I would have had a lot more to show you... ;_; rip... Also I died because I was getting pictures from the admins through imgur to bring this to you today... I am certainly robust... Definitely).
Now then...
Back tracking back to a usual hive in the NW caves. There are already a lot of walls and objects to hide behind, granted a few open spaces to fill with hivey goodness in the beginning. However, this is not just map design aesthetically, it is beneficial for the aliens to use tight and cramped spaces that promote close quarters combat to fight the marines! What sense does it make that a bunch of claws and jaws wielding bugs are going to run circles in a gigantic field trying to dodge a rain of metal seeds (hopefully at least in the darkness) from the marines when they could just... y'know... jump scare the shit outta them?
Now back to my game with the hive in the crashed shuttle...
We WERE surrounded by open fields, and as a strategy enthusiast this was just no good to me. I knew I had to become the hivelord, which the queen accepted thankfully as she started her crusade against individualism not too long afterwards... NONETHELESS. With caves to the east providing a decent amount of maze like walls to provide that nice advantageous CQC scene for our hive if it were in fact invaded through there, (unlikely since any salty non-suicidal marine would avoid going that route) I needed to provide the same advantages to the other side of our hive which at the beginning of the game was largely open like a giant ducking shooting range just waiting for marines to start spraying. And I did just that...

Finally, it is important to note while all this work you can put into a hive is nice and certainly effective it is useless if it isn't USED properly. Like I said, if it is not to be constructed in vain, aliens must play their approaches smartly. Hiding behind their walls when they can, or for as long as they can letting their prey get as close as possible and right before they're noticed they make their hug lunge. Better yet maybe try running around and through walls with other aliens like an episode from scooby-do to confuse or get them to waste their metal seeds on things they aren't going to hit. A patient hunter is a good hunter.
Thanks for reading!
TL;DR build lots of small walls for cover in open spaces when playing as the aliens and obey the queen.