Focus on Defensive Stats:

Life/ES (Energy Shield): Maximize your life or energy shield to ensure you can take hits from dangerous bosses and mobs. Consider stacking %life or %energy shield modifiers on your gear and passives.
Elemental Resistances: Make sure to Path of exile currency cap your resistances to the maximum value, particularly in higher-tier maps where elemental damage from enemies will be significantly amplified.
Physical Damage Mitigation: Investing in armor, evasion, or chance to dodge can help mitigate physical damage. If your build can, consider adding block or spell suppression as well to cover all types of incoming damage.
Life Leech or Regeneration: Certain builds rely on life leech or regeneration to survive prolonged encounters. Leeching from mobs or generating life through skills like Vitality or Regen can be invaluable during prolonged boss fights or dense mob encounters.

Flask Setup: Proper flask usage can mean the difference between life and death. Use flasks that provide:

Life Flasks: Instant or over-time healing.
Mana Flasks: For mana management during long fights.
Divine Flasks: These can remove status effects like poison, curses, or buy Path of exile currency bleed that may be applied by enemies.
Defensive Flasks: Flask mods that grant spell suppression, elemental resistances, or armor buffs can make you significantly tankier in harder maps.