Please feel free to edit and comment on what you think is a good team in DQIX. I hope you enjoy! (This is the type of team i use and has proven to work very well for me making grotto bosses and some legacy bosses easier for me.)
Minstrel / Armamentalist: This party member is well balanced in all areas and excels at supportive abilities such using egg on (assuming if this is the vocation your main character plays as since he/she can only learn egg on as far as i know) to increase tension and the 4 types of forces to increase resistance and offensive capabilities against certain enemies or bosses. This member also should invest some skill points in aquisitiveness to learn half-inch as other members can fight while stealing items from enemies.
Mage / Sage: This party member is very useful in offensive and a little bit of supportive magic (like oomph) in combat. Their low hp and defense can be fixed by investing points in vocations that increase those stats. They tend to have the highest mp of the group. It is recomended to spend skill points in spellcraft and enlightment since when the points reach to 100 (in spellcraft), magical might increases by 100, and when skillpoints reach 100 in enlightment, mp consumption drops by 25%. Note: Do not sell the dragon robe you need it to make the xenlon robe which is very helpful to get as it provides 42 points in magical might.
Warrior / Gladiator: This member of the team excels at defense and offense capabilities (in other words is the tank of the party). They also have through the roof hp which most of the time makes them last longer in battle than other party members. You should also give them the majority of your yggdrasil leaves and dew because of that. Gladiators tend to have less defense than warriors so be careful of that. Also, gladiators normally can't equip shields, but this is a minor issue since if 100 skill points are spent on the shield skill, any vocation can use one. Note: I recomend that this party member equips a meteorite bracer (which increases agility by 100) so they have a better chance to attack before the enemy.
Priest: This party member specializes in magical mending. It is helpful to invest 100 skill points on faith, since this increases magical mending by 100. Also, the priest should also invest 100 skill points in enlightment to learn right as rain and consume 25% less mp. If equiped with anything other than a wand, you will mostly find priests running low on mp quicker than mages. Note: It is critical to keep this party member alive since this is usually your primary source of hp recovery.