If you have difficulty advancing in the story, you'll have hard time because you'll need to do a lot of (boring) leveling.
I did it myself, I'm mostly leveling instead of enjoying the story at a good pace. I even went back to chapter4 after starting Chapter5.
I'll post my saves to filetrip (this weekend) if it can be useful to users who lost their progress (I kept a save for each chapters/crystal). though, I was busy and still haven't played my 3DS this month, I don't have saves from chapter5 yet.
- verify that the difficulty is set to easy.
- equip Bows (they are better than other weapons, even if you don't have Bow's mastery skill, or even if you are not an Archer).
- Set Brave x 4 (Attack x4) to all your characters
- Set auto battle (Y button), it will repeat the last action, so attack X4 right at the start of each battles
- level up like that for hours in place that you don't lose too many HP, but grants enough Exp.
If you end the battle on first turn, you'll get extra XP.