noob combo works just fine if you use the dexterity support package. also, get a feel for all of the new weapons as soon as possible. they're all extremely useful in the right situations. even the pulse grenade, which most people on here are saying is worthless but really it's extremely good. don't worry so much about rushing for the power weapons anymore either as the ordinance drops give everyone an equal shot at them. get the SAW every single time you see it, it's great at pretty much any range, even long distance on the medium sized maps. play defensively. most people are to aggressive, so you can pretty much let them kill themselves (jumping around while shooting, not paying attention. easy to place grenades where they land, or shoot them in the air while staying near a piece of cover. use your mic in team games. if you die with a good weapon, call out the location to your teammates. mix it up, don't just play slayer. dominion is really good, so is regicide. if you find teammates tht you work well with, send them invites for spartan ops. it's a blast and good team work is a necessity on higher difficulties.
oh and seriously.... play the campaign immediately. for my money, it's the best in the series. be sure to get all of the terminals, too. they tell a story almost as good as the main game.