Boss preparation is most useful when it removes avoidable uncertainty before the attempt begins.
Use a loadout you understand
Changing several systems at once makes it hard to know which adjustment actually improved the fight.
Know how you create recovery windows
Healing resources are only useful if your positioning and timing give you space to use them.
Learn one pattern at a time
Turn each failed attempt into information by choosing one attack or transition to understand better.
Fix the category that is actually failing
Change survivability, spacing, stamina or damage uptime based on what is ending attempts.