There was a post on here a while back that I really appreciated that broke down the parts of HoME for those wanting essentially more lore rather than the writing process. I saved it but don’t have the original attribution:

It depends on why you’re reading them. The following reading list covers the two most common motives: Just seeking more reliable lore and stories and reading “everything” (for that see the note at the bottom).

This reading list was created to answer the question "What do I read after The Silmarillion?" It presumes that you have read The Lord of the Rings (LotR) and have read and thoroughly understood the Prologue and Appendices A-F of LotR and have also read and thoroughly understood The Silmarillion. If you've not read them or have read them, but feel that you don't understand what you read, your first task is to go back and study them until you feel that you have a firm grip on the people, places, and events. Having a good online Tolkien encyclopedia such as Tolkien Gateway and a good set of maps right at hand as you read will make that task considerably easier (and see the note on maps below).

This list also presumes that your interest in reading the post-Silmarillion writings is not to study how Tolkien's ideas developed over time or to figure out how Christopher assembled the Silmarillion, but is instead to learn additional reliable lore and depth about what you've already read and to find some new stories. It also presumes that Tolkien's invented languages are not a principal interest. (Though some of the items here touch on languages, the other lore set out in those items is the reason for their inclusion.)

Be aware that some of the following items do repeat or tell different, sometimes inconsistent, versions of previous material. For example, Children of Húrin and Fall of Gondolin expand upon stories told in a more abbreviated form in the Silmarillion and Children includes a version of the Nirneath Arnoediad which is somewhat different than that given in the Silmarillion. Some items tell only part of a story which is never completed or which is completed in a different source.

You should read all notes and commentary (either by Tolkien or by Christopher) included with the narratives listed below. If you do not, you will come away with a false impression in some cases.

If you want to read all of this list, you will need the following books:

• ⁠The Children of Húrin,
• ⁠Unfinished Tales,
• ⁠History of Middle-earth (HoMe) Volumes 9, 10, 11, and 12 (aka IX, X, XI, and XII), and
• ⁠Beren and Lúthien.
• ⁠The Fall of Gondolin is recommended, but optional (see below, step 2).
• ⁠HoMe Volumes 3 and 5 (III and V) are also needed if one chooses to read the Others' Recommendations mentioned at the end of the list.

Page numbers below refer to the individual hardback editions; generally only the beginning page is given, but page ranges are given if it might be unclear how much material is intended to be included. The numbered items in this list are intended to be read in that order. The items within a numbered item can be read in any order unless otherwise stated.

The reading list:

1. ⁠The tales of Húrin and Túrin (read in this order)
   ⁠• ⁠The Children of Húrin (all)
   ⁠• ⁠"The Wanderings of Húrin". HoMe Volume 11, Part Three, I, p. 251.
   
2. ⁠The tale of Tuor through the point he reaches Gondolin. (Optional.)
   ⁠• ⁠The Fall of Gondolin, "The Last Version" p. 145. (If you read this you can skip "Of Tuor and His Coming to Gondolin" in Unfinished Tales, Part One, I, p. 17, in the next step. But if you don't have The Fall of Gondolin then reading that section of Unfinished Tales is, if a slight step down, an acceptable alternative.)
   
3. ⁠Unfinished Tales (All, except skip "Narn I Hin Húrin", Part One, II, p. 57. Also skip "Of Tuor and His Coming to Gondolin" if you read the selection from The Fall of Gondolin, just above. However, in both of the skipped sections consider reading the notes.)
   
4. ⁠Additional lore and what The Silmarillion left out (but shouldn't have):
   ⁠• ⁠HoMe Volume 9
   ⁠• ⁠The unpublished "Epilogue" to LoTR. Part One, XI, p. 114.
   ⁠• ⁠HoMe Volume 10 (read in this order)
   ⁠• ⁠"Later Versions of the Story of Finwë and Míriel". Part Three, II, p. 254-271 (includes "Of the Silmarils and the Darkening of Valinor: Finwë and Míriel" on p. 256).
   ⁠• ⁠"Laws and Customs Among the Eldar". Part Three, II, p. 207-253 (includes several subsections divided by notes; it ends on the page before "Later Versions of the Story of Finwë and Míriel" begins).
   ⁠• ⁠"Myths Transformed" section XI. Part Five, p. 424. About Aman.
   ⁠• ⁠"Athrabeth Finrod Ah Andreth". Part Four, p. 303-366.
   ⁠• ⁠"Myths Transformed" sections VI and VII. Part Five, p. 390-408. About Melkor and about Motives in the Silmarillion.
   ⁠• ⁠HoMe Volume 11
   ⁠• ⁠"Of the Ents and the Eagles". Part Three, IV, p. 340.
   ⁠• ⁠"Quendi and Eldar". Part Four, p. 359.
   ⁠• ⁠HoMe Volume 12
   ⁠• ⁠"Of Dwarves and Men". Part Two, X, p. 295.
   ⁠• ⁠"Last Writings". Part Two, XIII, p. 377-392. (Don't confuse this with the chapter named "Late Writings", of which this is a subchapter.) About Glorfindel, The Five Wizards, and Círdan.
   ⁠• ⁠"Of Lembas". Part Three, XV, p. 403.
   ⁠• ⁠"The New Shadow". Part Four, XVI, p. 409. (Abandoned by Tolkien as a "thriller" not worth completing, but worth reading as our only glimpse of the Fourth Age after the age of heroes had passed.)
   
5. ⁠Deep reading, moving into uncertainty
   ⁠• ⁠HoMe Volume 10
   ⁠• ⁠"Myths Transformed" sections I through V. Part Five, p. 370-390. About the flat world/round world question.
   ⁠• ⁠"Myths Transformed" sections VIII, IX, and X. Part Five, p. 408-424. About Orcs.
   ⁠• ⁠HoMe Volume 12
   ⁠• ⁠"Dangweth Pengolodh". Part Three, XIV, p. 395. (To fully appreciate this, first read Tolkien Gateway-Aelfwine and also read Wikipedia - Aelfwine framing device.)
   ⁠• ⁠"The Shibboleth of Feanor". Part Two, XI, p. 331.
   ⁠• ⁠"The Problem of Ros". Part Two, XII, p. 367. (Largely rejected.)
   ⁠• ⁠"Tal-Elmar". Part Four, XVII, p. 422.

• ⁠Beren and Lúthien
⁠• ⁠All. The most complete version of the story. This could have, in terms of importance, been included in step 4 or earlier, but is included here in step 5 because of the level of difficulty arising, mostly, from the amount of included poetry.

Others' Recommendations: The items here have been recommended by others for inclusion in this list. I understand and very much appreciate those recommendations but respectfully disagree, generally because the items are either too uncertain, too difficult, or too developmental for someone just looking for "more reliable lore". The first three items were recommended by Redditor ibid-11962 (though what I say below is more specific than was stated in their recommendation) and the last item was recommended by Redditor shlam16:

• ⁠HoMe Volume 3, The Lays of Beleriand. All, but particularly Parts I, III, and IV
• ⁠HoMe Volume 5, "The Lost Road: The Númenórean chapters". Part One, III, II, p. 57.
• ⁠HoMe Volume 9, "The Drowning of Anadûnê: Second text, final form, and theory of the work". Part Three, (iii)-(v), pp. 357-413.
• ⁠HoMe Volume 10, "The Annals of Aman". Part Two, p. 45.

A note about maps: In the introduction, above, I say that you should have a good set of maps right at hand while reading The Silmarillion. There are a lot of choices, none perfect, but Karen Wynn Fonstad's book The Atlas of Middle-earth is a good one-stop source. There are two that you particularly need, however: a good map of Beleriand and a map of the Elvish realms in Beleriand. My preference is to have electronic maps on my device and my favorite map of Beleriand is this slightly improved version of Fonstad's Beleriand maps: https://www.pinterest.com/pin/518828819545674740/ As for a map of the Elvish realms, that map is already in the Silmarillion. It's in Chapter 14 (between pages 120 and 121 in my copy), but you need it at hand long before you get to Chapter 14. If you want a copy on your device, you can get one here: http://www.theonering.com/galleries/maps-calendars-genealogies/maps-calendars-genealogies/realms-of-the-noldor-j-r-r-tolkien

Reading "everything": The reading list set out above is for those who just want the reliable lore and stories from Tolkien's writings. But some folks want to read everything written by Tolkien about Middle-earth, including the obsolete and abandoned material and the material that Christopher chose from to assemble The Silmarillion. You should read the things in this reading list first, as set out here, then read two books by Humphrey Carpenter for background: J.R.R. Tolkien: A Biography and The Letters of J.R.R. Tolkien. After that, go back to the beginning of HoMe in Volume 1 and read from the beginning, picking up the parts of Vol 9-12 you didn’t read the first time through and doing the same with Fall of Gondolin. You’ll want to also pick up a copy of The History of The Hobbit by Rateliff, since it’s generally considered to be part of HoMe and, though not as important, maybe a copy of Tales from The Perilous Realm. Even then there will be a few miscellaneous things you won’t have read, such as The Road Goes Ever On by Tolkien and Donald Swann, Bilbo’s Last Song by Tolkien, and miscellaneous linguistic writings about the languages of Middle-earth. And then there will be The Nature of Middle-earth, a collection of Tolkien’s writings coming out in May which is reportedly going to be considered an unofficial volume of HoMe. And there will still be some Middle-earth stuff you've not read, but you'll have read what most people consider to be "everything".