Terraria at it’s core is about boss progression.

Here are the mandatory ones in order of completion:

1. Wall of flesh
2. 3 Mechanical bosses
3. Plantera
4. Golem
5. Lunatic Cultist
6. Moon Lord

The rest is prep work for each one.

• Collecting NPCs and making housing for them
• Collecting weapons, armour, accessories
• Building arenas for bosses
• Building farming locations
• Defeating optional bosses for more powerful loot
• Grinding defeated bosses for specific drops

What I usually do is:

1. Build starter house
2. Go mining
3. Go exploring
4. Beat corruption/crimson boss
5. Make a hellevator
6. Make wall of flesh arena, beat it with dynamite
7. Lots and lots of gear grinding
8. More prep work for mechanical bosses

The last 2 repeat for each boss that’s on the list and often include beating other bosses or events for their loot.