Because of the recent par score changes, this particular score is now fairly easy to obtain by playing the level on Heroic. Par time is your friend here, but you have to be good enough at the Warthog Gauntlet.
You won't earn many points during the Gauntlet, so make sure you at least 18000 points before you take the elevator. If not, I'd recommend restarting the level then and there.
After messing around after the score changes, I would recommend doing it on Heroic as Normal difficulty would require quite a few skulls (I had 12k by the elevator on Normal 2 skulls on, and that was with no deaths.)
If you're going for the par score I'm assuming you at least know the level but here are just some points to add.
In the beginning when you have to wait for the door to break, at least 1 enemy (who comes out the door) will have a shotgun. Make sure you grab it. The shotgun should 1 shot a hunter as long as the whole blast hits the orange bit. The shotgun sucks against the sentinels, however, so I would recommend either keeping your plasma rifle from the beginning or grabbing a plasma pistol.
When you get to the engine room, make sure you pass it to go to the armory. Swap your non-shotgun for a rocket launcher.
When you do the engines, I would recommend going up the right side, as the left is more annoying with its infinitely spawning enemies. Both ramps have infinitely spawning enemies after you blow up 2 of the engines, but I found the right side more bearable.
When you blow up 2 engines, head towards the elevator so you can get a checkpoint.
Don't hesitate to hide when the sentinels come out as its hard to fight them with a rocket and shotgun.
When doing the warthog gauntlet, make sure you skip the wait for foehammer and go to the side during the ending run so you aren't caught in the crossfire.