Clear out an area before fighting a golem. Jump attack them with a pickaxe so you don't pickaxe the ground. I always dodge roll them then circle around and jump attack. Repeat. They move slowly so if you get adds run off a bit, deal with the adds, then come back to the golem.
Set up a fortified mountain outpost with a portal. If you put in on a nearly sheer cliff section, like on top of a large rock outcrop it'll be immune to most attacks except drakes, which won't attack it they can't see you.
Never ever be out at night, the enemies are much stronger.
When you're mining set up a work bench and some torches as both items create a 20m no spawn zone. This helps lessen the chance of getting adds as they can't spawn close by.

And finally, if you think the Mountains are bad, just wait for the plains.
The Mountains are a cakewalk in comparison.