Spells to use:
Gravity (-5% evasion) [Wind Staff]
Paralyze [Ice staff]
Dia II or Bio II (depending on mob) [Light staff or Dark Staff (respectively)]
Slow (If you have pld tank use this spell, if nin tank, if theirs doesn't stick use this spell) [Earth Staff]
Blind (If pld tank, blind taken care of, if nin tank, if theirs doesn't stick use this spell) [Dark Staff]
Poison II (If blm doesn't take care of it) [Water Staff]
Frost (If no blm) [Ice Staff]
Conserve MP and use your spells wisely. Also, don't take up back up heal to much, rather now with ur newly aquired haste, help the whm haste the PT (I usually /tell the whm before we start and ask who they want me to haste in the PT). It saves the whm mp some and it doesn't differ between mp each time (unless conserve mp), so it helps you with controlling mp and using convert wisely.
As for what staffs are good to get, in order of importance:
Dark Staff
Light Staff | Wind Staff (equal importance i feel, as gravity is an amazing spell)
Ice Staff (Good for bursting Distortion)
Earth Staff (Slow and its good for solo because ups enhancing skill for stoneskin) On the verge of optional i believe.
Optional:
Water Staff
Fire Staff
Thunder Staff
The other staffs which i forgot.
*edit*
Ok, now that im done with that, i forgot to add, DON'T WASTE MP ON CURES. That doesn't mean don't ever cure, that means, watch your mp and know your limits (meaning how much mp you need for your next round of refresh and enfeebles on the next mob). What i usually do is, if I see someone in yellow, i'll throw a cure that will get them out of yellow (or just give them more hp so the whm can get them outta yellow), don't try to cure them full.