First boss is scary, but heres some tips if you're a warrior.
First: get the guy to teach you shield bash
second: level up your stab
third: don't fight the bats, just go through the tunnels
Fourth: on the tunnel with multiple choices, go up
Fifth: heal yourself all the way
Sixth: arm yourself with shieldbash
Seventh: use shield bash, and rapidly
stab.
When he breathes fire, just bash him again