How to complete Zelda II:
You must gather all of the crystals by completing the dungeons and wake up Zelda. If you lose your lives the game is over, and Ganon returns.
There are many strategies to make this game easier. I like to level up the attack first, so enemies are much easier to kill. Then I balance out magic and life once I get my attack to 8. Speed runners often skip a lot of objectives, like getting the candle so you can see in the dark and gathering other heart containers.
To get the most bonus experience possible, try to gather much experience points before you complete the dungeon so when you place the crystal, you get the most points and you don't have to farm experience. For instance if you have attack 4, magic 2, life 4 and you want to level up attack again, cancel out the magic and life when it asks you. When you place the crystal, you will get 2000 experience and level up attack to 5.