What do you do first?
Beat campain
or
Play multiplayer
The VERY first thing i will do as soon as i put the halo 4 disk in, is check out forge, and have a look at the new weapons and vehicles, and have a quick scroll through the new forge items, and check out the forge worlds.
Then after a couple of minutes of that, ill go straight to campaign on legendary, and as soon as i finish the campaign, ill go to multiplayer.
Check out all forge maps and tools. Then wait until my friends are ready to embark on the Chief’s new adventures!
how many of these threads is that now
Play maybe one or two missions on legendary, play some multiplayer, beat a mission of spartan ops
100% legendary campaign…
I’ll start campaign and then break for some multiplayer. I’ll be in a party though to avoid people screaming any variation of the following.
“Chief dies at the end!”
“The Arbiter is back!”
“Chief blows up Requiem and then blows up another Halo ring!”
Campaign first, 4 player co-op with friends 
Best way to finally know what happened to Chief without getting some lousy spoiler online, and a great way to get to know Halo 4 gameplay and weapons before I get online. 
> 100% legendary campaign…
This
How about this keep up in all lists at the same time read for details
Campaign, without a doubt. It has the most canonical factors in it, plus it helps the books.
Campaign and spartan ops on normal(so as not to die too much :D) then Multiplayer.