Below is my boss fight about a month ago. Took less then 4 minutes to bring her down wearing leather armour, wielding a Crude Bow, and used less than one stack of regular wooden arrows. Skip to 1:08:06-ish for the boss fight near the end of the video.

https://youtu.be/Nsp99dV2x2U?t=4086

I ate Raspberry, Honey, and Cooked Boar Meat before the fight.

Tips:

1. Do not summon the boss near your home. Who does that and why? Make your home farther away.

2. Scout the area around you and see how you can use the terrain to your advantage.

3. If you're still at your first boss, just restart the game. The video above shows me playing for 5 in-game days before confronting the first boss.