Area 1: Buy the Katana as soon as possible.
Area 3: Use all your money on upgrading your sword and use the bonus points to increase the length of your sword.
Area 4: Buy the magic missile, because the gas clouds and the end boss are immune against everything except magic.
Area 6: You can hire Indigo Roger at the Oasys.
Area 7: Don't worry about the pyramid, you won't be able to enter it until you make it to area 13. The Pyramid contains a Doppelganger which drops the Energy Blade.
Area 9: Eefrets weak spot is water. Kill Poseidon (stage 7) a few times until you got 10+ aquamarine juwels and spend them on your sword (xefrk the Enchanter in stage 5).
Area 10: Most enemies here are weak against fire attacks, including the boss.
Area 11: Buy the coin of bravery before you fight against the Necromancer or else he will push you off the battlefield.
Area 12: There is a location called Secret paradise at the east side of the forest. You can hire NIN NIN there, who heals you during fights.
Area 13: In the battle against the ice queen, you need a fire sword and a water armor.
Area 14: When fighting against the Guardian Dragon, you should use a water sword and a fire armor. When you aim at his feet you're in a position where most attacks miss.
Area 15: The Demons in Steeple of Mlq drop a lot of money. When fighting against Death, you should use a light sword and a dark armor.
In the location with the Living Armors, there is a very rare enemy called the Golden Knight which drops Hyper Armor. Hyper Armor has 9999 Fire, Earth, and Light protection.
Area 16: The Watchdog's main attack's size is based on your sword's size.
After the Watchdog: You can use the bone Watchdog drops to hire Wan Wan in Area 1.
Equip the Trophy dropped by False God and the Shrines will change into enemy locations that require tricks to solve. In the Strength Shrine, keep attacking the wall until it dies. You may need to unequip magic. In the Vitality Shrine, do not attack the Pixie. It will eventually just die. In the Intelligence Shrine, walk over the multiplying slimes to pop them. In the Luck Shrine, walk around the money bags to find the one real one (100 G). After beating the Shrines, the Trophy will glow. Equip it and walk off any side of the World Map to go to the moon which has the final boss. The final boss drops a ton of gold, emeralds, apples, and the Order of the Star item which when equipped puts you in hard mode.