I did this to get massive amounts of points, and leveled up like crazy.
Alien mission 7: Stalkers
When you start follow the arrow to the next room. In this area a Yautja (Predator) will watch you fight a few enemies. After you are done killing them you have to climb a wall.
Here is where the tip I'm giving you is.
Once up the wall you will see an enclosure/ a fenced area.
Now go to the right slowly. There you will see a sentry gun firing on alien enemies.
Don't go too far out or the gun will fire on you.
Once the enemy aliens come after you, go into the fenced area and pit yourself in between the boxes, and fencing in the bottom right corner.
When you go back into the enclosure the enemy will follow you. Then more will come, and more, and more. Eventually you will be over run by them then can't move.
The thing is if you are in that corner, the amount of alien congestion, will stop most hits on you by them because they are too close together.
Here's the "fun" part.
Now you can either swing away at them by holding "a" down. Or you could combo them by hitting "A" three times then hitting "B". This will cause your alien to jump and slam his fist to the ground sending enemies flying. This will either cause mass kills or just knock them back a little.
The alien enemies at this point keep spawning forever (until you get past the sentry gun to the tunnel to the right which will stop their spawning) so there will be no shortage.
After doing 1 mission I leveled up to 35 and received 3 million Xeno points.