All around post launch window
3 i just did with a buddy online as we were both starting it almost the same time. It really isnt that bad. Just 2 evenings about 3 ir 4 hours each? Some times we just farted around. We had fun though.
Odst i did solo over 2 afternoons, same as halo 4.
Then we come to halo 1 and 2...
Ce i got through to "keys" and was halfway through the level solo and my playlist reset...Got about halfway through again, reset -Yoinking!- again.
Halo 2. I was i believe either just finished regret, or on the last "checkpoint" solo. Somewhere around there. -Yoinking!- reset. Go to about mid point into the campaign again, and fricking reset.
Then the checkpoint sharing workaround came to light, so i did those for halo ce and 2 just for the achievement then just went to level select and continued from where it had reset and did them that way. Besides them resetting 2x a piece each it wasn't absolutely that bad. Primarily did everything solo, ce and 2 obviously took me the longest overall even without counting the resetting.
3, 4 and odst my first playthrough on each was laso.
Looking forward to Reach laso.....except the last fricking level. >_<
As for tips. Use guides everyone mentioned above.
Have some patience.
If you are getting frustrated at a particular "checkpoint" than take a breather and either play a quick match or 2, or a different game fir 10 or 15 minutes, relax, then try again. Getting more stressed than needed(these are a bit stressful to begin with) will make it harder.