The Sil is challenging, no question, especially diving right in with the Ainulindalė and the Valaquenta, which can be like cracking open a King James Bible from an alternate dimension while you're trying to kick back on the beach on summer vacation. I don't know if I would have ever gotten through it if it wasn't for wanting to be able to keep up on these here Downs. I'm glad I did, though the Sil will never be the sort of comfort book that LotR is for me. My experience reminded me of reading
Moby Dick -- the work you put in slogging through the first third or so pays off in spades on the back end, and once you get comfortable and conversant in the world of the First Age, you can go back and appreciate some of the poetry in the earlier chapters.
Some good advice has been given in this thread. I'll echo the things that ring true for me:
- Have easy access to maps and family trees. For me, having a couple of extra bookmarks so that I could easily flip to the resource I needed was enough.
- Have a nice chunk of time to devote to it. The Sil is not the type of book to read in small sips, ten pages before bedtime or something.
- Hang in there at least until you get into the first few chapters of the Quenta proper. If you can get to chapters that have actual scenes and exchanges of dialogue and a narrative thread, you can keep your head above water.
I'd add, don't approach it as a duty. If you love Middle-earth, you probably owe it to yourself to give the Sil a shot, but it doesn't make you a bad Tolkien fan if you never warm up to it.