I’ve played halo since around 2008. I love all the games and I’ve been itchin to beat all of them on Legenday! I just need some tips for legendary difficulty and some overall tips on how to be good at improve my skills at halo. Since I’m around average. Thanks!
Look up playthroughs and if those dont help look up speedruns.
Me and a friend are in the same position as you so I have nothing to say sorry.
Noob combo (plasma pistol and Magnum/BR) is your best ally.
Halo CE:
- Patience, try to prioritise targets. You can clean up Grunts and Jackals easily to then deal with the Elites.
- Grenades only for indoor kills or if you need to force an Elite to roll away
- Learn where the enemies tend to spawn and learn which area’s you have to push through (like The Maw)
- The Library there are a handful of sections where you will need to defend. Put some distance and use the Magnum. Save your Shotgun for the final defence section and try to funnel the Flood into manageable areas.
Halo 2:
- Noob combo can easily do most of the work for you. Headshot capable weapon, preferably BR or Carbine + PP
- Learn the enemy spawns. Jackal Snipers are way too overrated in the community and are always in the same locations. If you know where they spawn, they are nothing more than a small threat.
- You can abuse speed running shortcuts to skip some more troublesome sections
- Patience is rewarding
- Active Camo as the Arbiter can help you bypass alot of fights.
Halo 3:
- You can abuse the Noob Combo if you like
- Pick off the weaker enemies first.
- Learn the encounters. Ghosts are criminally accurate this time round so be careful when dealing with them.
- Most of the game is surprisingly easy even on Legendary. You should have very little issues if you follow the above.
That’s my advice, hope it helps. Good luck.
for CE get familiar with the levels, if your teammate dies find a safe spot to respawn him (if in doubt, crouch-thank me later), plasma pistol works wonders, needler also
as for fighting the flood take your time, good luck on the library (not that hard once you get the hang of it), you will also need luck
for Halo 2 (hardest campaign on legendary), noob combo everything, you need to work with your teammate; if one dies you go back a checkpoint, dont rush things, wait for checkpoints, you can also use some skulls to your favor, as for the sniper jackals; i hope you have a lot of patience
Halo 3, its so easy to beat legendary i could do it with my monitor turned off
P.S. youtube has countless guides on beating the Halos on legendary, have fun 
I just wish that I could do it on laso but isn’t that way harder especially with iron.
I would look up guides to show you the right path to take, even skips and despawns.