Here is how to kill him easily:
1. Use Silver sword as spirit damage is useful on Yagluth.
2. Use fire resistance mead
3. Bring health and stamina potions
4. You can hide under Yagluth himself from the meteors. His head will block most of them.
5. Try not to stand in the blue fire if you can avoid it. The initial blast itself can be blocked as of H&H.
6. If you need to regen and your potion is on cooldown, keep an obstacle between you and him, but watch out as he might laser through it if the distance beween you is too high.