Don't forget, using certain types of spells, weapons and specific jobs can boost your(and your party members) damage against espers. I believe it also gives you more points for your rank or w/e. What stuff boosts it changes every day though, but anyone in your brigade can reveal that information and let everyone else know.
Current Player rank: 226
Brigade Rank: 25
Just started today and already almost at the same rank I had before...