Final Fantasy I & II Advance

To do extra damage, take any damage doing spell(such as Fire, Ice or Holy)
Now go into a fight with only one monster and when your aiming your spell hit up to target every monster (even though there's just one) and attack. you do 1.5 more damage then if you attacked with it aimed only for the solo monster, because the way this damage is done is (Spell damage)x 1.5/ by the number of monsters

You still get the 1.5 boast to the spell, but it is divided by 1, thus not lowering its damage compared to if there were 2 monsters.

While on the ship, hold down A and keep tapping B. Soon, a sliding tile minigame will appear. The aim of the game is to put the numbered tiles in order from 1 to 15. If you do well, you gain items and money!

Simply attack yourself one or two times, and your HP and/or stamina will be raised after almost every battle. Im REALLY early in the game and i already have over 1000 HP for each character, and it barely took me any time. As an added bonus, your weapon levels will also be raised.

In the Water shrine, go in it and find the area with all the dancers. Talk to alot of them and you should hear some say something about the Tatarus theater and the "I want to be your canary" play which is all Zidanes theater group in FF9!

In Final Fantasy I when you visit Elfheim, press A on the left most tombstone behind the inn. It will say "Here lies Link." Link being the famous star of the Legend of Zelda series.