Here's what I've come up with for Exe Create games, where you have the option to adjust the Difficulty settings, and the encounter rate:
Note: this is not my area of expertise, as I'm usually more a casual player, and have often finished games on Easy because the battles just get too annoying. But I've done a little bit of testing and this approach seems to be solid. (Although I'm sure there are better ways to go about it.) My opinion is, you shouldn't start this until you have all four or five party members, but perhaps you could do it at the very beginning of the game.
1. First, always start the game on Easy (unless for some strange reason you really want to get owned on the first random encounter, then start on Expert

Turn "Battle Shortcut" on (where available), and if you can set the Encounter Rate, put it as high as you can.
Sometimes you can adjust the Encounter Rate in the Options menu, and sometimes you need an accessory like an Encounter Ring where you get an encounter with each step. If you have an Encounter Ring this will go a lot faster (and in fact, if you don't, this strategy may not be worth the time it takes.)
2. In whatever location you start this in, keep fighting random encounters on Easy until one of two things happens:
2.a. You can handle most encounters on Auto, or
2.b. The Battle Shortcut kicks in, and you cut straight to the result screen.
3. When you can easily handle the encounters on Easy, change the Difficulty to Normal, and repeat the process until you can easily handle Normal.
Repeat for Hard and Expert.
4. When you can easily handle Expert mode, finish exploring that location, and when you go to the next location leave the Difficulty on Expert.
If the enemies become too powerful, change back to Hard, or Normal, or Easy, and then repeat steps 2 and 3.
You can do this as early in the game as you like, and if you decide later on that you'd rather just play on Easy or Normal, well, you'll most likely be quite overpowered for awhile. B)