Well, there is a lot to cover when it comes to such a triology of this magnitude. You can base it off the landscape, picking key moments in the history of the book, even events in the storyline. Moutain of Mordor, the one ring, you have the ring wraiths, those giant eagles, you have the fellowship, the city of gondor, the fortress of helms deep, of course, Gollum, then you got the elves, the dwarves, humans, hobbits, the shire, and practically almost anything of that sort, Rivendell, and the Mines of Moria. My
Then again, you could look at it as light and dark, you have the orcs and goblins and trolls, and mordor, and Saruman on one side, and then you have the fellowship on the others, the ring in the middle. In the end, this is just me talking, and it will look far cooler than any idea I can bring up. I hope this inspires ya.
P.S. My friend loves the writing styles of elves and the like. You could always find one of those online... google search, and they will most likely have the whole alphabet.
Yeah, I think it would be really cool if there's a concept instead of just a huge collage of everything. I will be doing the front, back and also sides of the guitar (acoustic), and I've already thought of writing the inscription on the ring around the sound hole of the guitar on the front - so I guess I'll put all the Fellowship related things on the front side? Or, I could position elements in relation to the map of middle earth...