When in a battle and there are stumps, crates, etc., attack and destroy them. Sometimes you will get items and Spirit Stones. It is worth the extra effort because even if it is empty, you get experience and SP for them.

When you are in the Flying Castle and are fighting Lilia Getmann, there will be a few Meshimgen. If you kill one, on Lilia Getmann's next turn it will summon another Meshimgen. With this strategy you can get incredible experience and SP. The Meshimgen also will usually drop 60 Spirit Stones, so you can use as many skills as desired. With this strategy, you can level up, get more Spirit Stones, and have enough SP to get everyone's star number to the maximum; allowing you to get ready for the powerful final Boss, Lord Of The Black Abyss.

An very easy way to get extra experience is to fight in the Arenas (Cathena and Lamda in Kharg's story, or Orcoth and Rueloon in Darc's story). Although expensive (100 G for five to ten fights, 200 G for fifteen to twenty fights, and 300 G for thirty fights), you can sometimes get 5,000 experience per fight and upwards of 100 SP. A good strategy for getting though them is to make sure you have enough Spirit Stones or items to keep yourself healed. Also, remember that the final round is more often than not the most difficult of the entire competition.

After unlocking the New Game+, in Darc's second chapter, go to the Orcoth Arena and equip who you want to level up with the Romantic Stone. Then, enter the second tournament and use only skills. Because of the Romantic Stone, it will not use up Spirit Stones. You can go all the way up to level 40 in a matter hours with this strategy.