So, since you haven't responded yet, i'm just going to type this up under the assumption you've never consumed any Halo media before, so
As a short tl;dr so you know what i'm talking about and have some context, most of the halo lore takes place in the 2500's, where humanity, having a small interstellar empire controlled by a totalitarian military regime (the UNSC), gets into a civil war(the insurrection) after the outer colonies desire independence. However, midway through that, an alliance of alien religious fundamentalists called The Covenant that worship a long dead alien race discover humanity, declare them heathens, and start to wipe humanity out. Most of the Halo novels are what I like to call "Firm" sci fi. It's not quite hard sci fi, but it's not science fantasy/soft sci fi either, it's sort of in the middle.
It's perfectly possible to get into the books without having played the games, and you can get through around 5-6 of the books before needing the games, but after that point it's going to start to be seriously detrimental to your experience without having played through the games or watching them on youtube.
I'm going to split this into at least 2 posts: The Bungie era (2001-2010) and the 343 Era (2011-present). This is because the shift represents both the franchise going from Bungie to 343 Industries, as well as what the media focuses on and wheras with the bungie books, there's a clear obvious order, for the 343 books, it's more complicated.
For the bungie era stuff, I recommend an order of
Fall of Reach > The Flood/Halo CE > First Strike > Ghosts of Onyx > Halo 2 > Halo 3: ODST > Halo 3 > Contact Harvest > Halo Wars > The Cole Protocol > Halo Reach > Halo: Evolutions.
The stuff in spoilers are games instead of books. You don't NEED to play the games exactly where I have them, that's simply the ideal, but after the cole protocole you will need to have played at least the main game trilogy (Halo CE, 2, and 3) before moving on, or at least watched them on youtube. In general, I'd heavily recommend though that you finish all of the above before moving onto the 343 media.
Also, tFoR, TF, FS, and Evolutions have reprints. You should try to get versions of the first 3 that have the following covers, and even better, the "definitive edition" label, but if you can't find one with the definitive editon label and only the new covers, that's fine. For evolutions, the reprint split it into 2 smaller books, called volume 1 and volume 2.
1/4(?)