LITERALLY JUST DO THIS:
All Skulls but blind (Kind of handy just to see your shields)
At start find a nice open area and kill the grunts with DMR headshots run to the elite/s melee once then try to get behind him and assassinate him(get used to doing this)
keep doing this to every elite that comes up to you until the General Elites start coming(Yellow big fellas)
Once these Generals show up just keep trying to chain assassinations and get one of their swords, keep an eye on your shields if they are low just get a hit or two in with the sword and then continue with the assassinating.
This method will take a while so maybe have a small break here and there and after you have over 150,000 points let the elites....
edit: there are barrels around the place so you the area you have chose has them... stand back and shoot them a couple of times or it could be you also restarting because of them.
note: you can try it on normal for more score but I found the elite ultras would be able to down your shields a little bit too fast to be able to melee them for shields.... might've been a little drunk to handle them at the time.
Here is a video if you need, shouts to the General, go and check out some of his other vids while you're at it