Make poison resist potion.
Eat serpent stew, turnip stew and sausages
Be well rested
Start fight early, clear area of any spawners
Use mace, blunt weapons for highest damage.

To cheese
Use hoe to bring up ground around boss spawn
Build a hut on top of spawner skull or in a tree
Shoot with frost arrows

still need help?

Use mace, start fight early, clear any spawners in the area, be well rested, have enough poison resistance mead, and eat the best foods you have are all good pieces of advice.

You probably won't be able to access the materials to make frost arrows, since they'll require harvesting several resources from the Mountain biome. However, if you can access obsidian and frost glands from dead drakes, by all means do it that way. A friend and I took down Bonemass in less than six minutes with frost arrows. Of course, you can also play at being a (possibly dead) hero by doing it harder ways, but if that's not necessary, it's nothing more than vain and empty egoism. And if you don't rearrange the landscape to your convenience, here and everywhere else, you're a fool. You were given a ridiculously powerful pickax and hoe for a reason.

I wouldn't build on top of the spawner skull, though. Bonemass will just smash up anything there. Find a nice location off to the side a bit and build yourself a base camp. The trunks of large felled trees provide excellent cover since nothing in the game can smash them, and only blobs can jump well enough to get past them (sometimes; wraiths fly over but only at night). If no tree trunks are available in the right place, then dig you must.

If you just can't be content unless you do something daring and enterprising, find a patch of Plains biome and sneak over the border to pick enough cloudberries to make medium strength stamina mead. Even better, kill a few lox for their meat. If you're lucky, you can find a herd that are grazing right at the edge of the Plains biome and kite them out of it before the Fuling and the deathsquitos notice that you're there. When killing lox, once again it helps to pull out your pickax. They are tough and fast, but incredibly stupid, and it's not hard to lead them into traps by digging a few ditches. If the gods are smiling, a charging lox will get stuck in a ditch and you can take your time shooting it to death. Don't try melee, though; they can stomp you quite easily.