In the Stronghold of Security, fight the weaker Minotaurs with 10 hp, just shoot a bunch of them with low level spells.
you use range or use mage... depends what lvl you are
where are you at right now? if you're done with bahumut, the pharos are the best place to lvl.
Edgeville dungeon
The best place to train a lvl 20-30 Lucario is up by Snowpoint city. Fighting types like him are really good there.
go to walic's shop and click on mage quests then click on wizard quest (you have to be a lvl
you should train sycher against fire and pshcik pokemon:D
henesys party quest till lvl 21 then go kerning party quest
Rock crabs in relleka would be the best way.
Try the grass in Lilycove City, or go train in Victory Road.
what i did was train your team in mt. cornet or around snowpoint city because there is really good Pokemon around that area. hope this helps :)
You can train them up at victory road or on the way to the survile area
just continue battleing in a patch of grass with lvl 30s