LogFAQs > #950021681

I'd recommend making an arena at the spawn point (where you go when you magic mirror). It helps a ton for fighting bosses and invasions. Just create a decent sized flat surface, try to fill in the area underneath the ground so enemies are less likely to spawn there, and make multi-level platforms that you can jump up and down to avoid enemies. Space out some campfires and heart lanterns for faster heals.

Avoid crimson/corruption areas until you have a handful of extra hearts and some decent armor. Should also avoid jungle for a while. Explore the surface until these areas gatekeep you out, then start searching underground. You'll want to bring ropes, wood platforms, and (lots of) torches when you go down. Carry some glowsticks too, can save your life if you fall into a dark cave filled with water. You should build your tunnels somewhat nearby your home base so you can haul loot back up easier.

Also be sure to take the chests you loot with you, you'll need somewhere to store items and materials. Its never too early to start organizing, try making a rows of chests for different purposes; one row could be weapons, next could be ammo, items, potions, materials, etc.

You'll probably want to look up bosses and how to summon/encounter them, since it can be pretty obscure sometimes.