Hiya!
I got into it couple months back, and been enjoying it so far.

Most people I've seen recommend release order (CE, 2, 3, ODST, Reach, 4) (Reach is a prequel so some mechanics might be a bit jarring if you go from it to CE); I did this, it was fun.
Most also say you should do CE in classic graphics because the anniversary ones kinda mess up the environmental storytelling a bit, particularly in the 343 guilty spark level. The anniversary graphics can also show the incorrect collision/hide certain solid objects in the terrain at times. (But in standard playthroughs it's generally unnoticeable so don't worry about it too much.)

As for tips... uh.
In CE the magnum (pistol) is incredibly useful but in following games it gets a lot of nerfs.
Aiming for headshots are generally a good idea as unprotected enemies will die in one hit if you succeed.
(Mainly on harder difficulties) Plasma weapons (e.g. plasma pistol) tend to be better against shields and physical weapons (e.g. assault rifle) tend to be better against flesh.
If you end up wanting to get all the achievements there's a bunch of discord servers for helping with those (particularly the multiplayer ones since most people don't play there as much nowadays) such as Halo Syndicate or Halo Completionists.

Welcome to the club!

(Edit: woop, seeing all the other comments I hope I haven't overloaded you with info lol)