Restoring Hope - Taking Nelson
I guess it's possible for this to complete instantly if you've already killed Dead Sea while rescuing the captured and crucified NCR troopers. If you have no idea what I'm talking about, then you're fine. Note that sometimes the quest will just bug out and not recognize that Dead Sea is dead, which means that you probably just won't be able to finish it up. Just keep your fingers crossed that the triggers register right.
As for the actual assault, it's pretty easy. Just bring a good assault rifle (I brought a new LMG that I bought from the Gun Runners to make it extra fun, but you really don't need that much firepower), and preferably a good companion. If you're Pro-NCR, then there's no reason to not bring Boone with you for the attack. Polatli will send you out to join up with three NCR troopers. Talk to their leader, Cooper, and you can follow them to Nelson. You'll have a brief engagement after meeting up with them, but it should be a straight run to the base after that. Try to stick close to them and help them break right through the perimeter. There should be at least one guard behind the sandbags in a good firing position, so try to snipe him yourself to keep the troopers alive.
Watch out for melee rushers and enter Nelson. There actually shouldn't be that many Legion guards inside the camp, so just try to keep moving and firing. Legion guards seem to come in pairs, so as long as you fire quickly you'll be fine. They actually shouldn't be armed too well. On the other hand, your troopers should at least have service rifles. Hopefully it will keep things balanced.
Your target is to just kill Dead Sea inside the main barracks. The NCR troopers with you will make a beeline for it themselves. Dead Sea will probably try to attack with his unique machete. If you've got a shotgun and good aim, he'll fall apart really quick. He should also be by himself for the most part, so just take him out and collect his gear. Once he's dead, you're basically done. You may want to go ahead and finish off the Legion soldiers in the other barracks.
Note that you should check the NCR soldiers, since I believe some of them will have dog tags that you can give to Quartermaster Mayes.
Finally, if you didn't do the quest already, and there are still three NCR members crucified in the center of camp, untie them and set them free for some NCR rep and a lot of points with Boone. This is a pretty good way to get his companion quest.
Report your success back to Major Polatli to complete the questline and fully restore Camp Forlorn Hope.