I mostly used physical attacks and Agrias' sword techniques to fight. However, I also used Geomancer's abilities to soften up the enemies until I got my fighter characters close to them. Another strategy I used was a Summoner with Short Charge. Basic low-level summons, Titan, Golem and healing summons were especially useful, and IIRC, the Summoner gained EXP somewhat faster than the others due to such summon-spamming.