Try to xp your NPC on mobs at that are least five levels or more above your
NPC's level when your NPC is level 30-45, six levels or more when your NPC is
is level 46-50, seven levels or more when your NPC is is level 51-55, and
eight levels or more above your NPC's level when your NPC is is level 56 or
higher.  The higher the better.  On this chart, go by the first number for
level.  Mobs may not always be higher than their minimum levels and can thus
hurt your NPC's xp if you go by the second number.  The monster data was taken
from http://ffxi.somepage.com/zonedb/ .  The solo xp vs. mob level data was
found at http://ffxi.somepage.com/links/exp_table.html .

When you fight, try to keep the mob pointed away from your NPC.  Especially
with you are fighting mobs that uses coned or straight-line attack abilities
like Ogreflies that has poison spray and the like (crawlers, leeches, and
tigers also come to mind).  Also, mobs with strong AoE attacks, especially
those with suicide moves, can be bad too (such as goblins, Ogreflies, and
weapons) (thanks Icemage).

As stated elsewhere previously, avoid mobs with pets.  This includes Bst, Smn,
and Drg mobs.  A quick list of these mobs includes Goblin Traders, Rime Gigas,
Demon Warlocks, Frost Gigas, Goblin Enchanter, and Hobgoblin Animalier.

Be careful of Blm, Rdm, and Drk (not so much Drk) mobs because they can sleep
you and kill your NPC if they get hate. Before engaging, you may want to use
range or magic attacks on them to be sure that you don't lose hate if you get
slept.  A quick list of these mobs includes Ghasts, Demon Wizards, some Lost
Souls, Antican Retiarius, Antican Speculator, Antican Lanista, some Cursed
Weapons, Ominous Weapon, Hobgoblin Fascinator, Hobgoblin Alastor, Hobgoblin
Toreador, and Lich.  Some Blm mobs can also use elemental spikes which can
harm your NPC significantly if the NPC's level is too low for that mob.  Ice
Spikes are particularly bad because they can paralyze not only your NPC, but
you as well.

Finally, please note that "a player fighting with an NPC fellow will receive
only 70% of the usual experience points gained for solo battles."  As stated
at http://www.playonline.com/pcd/update/ff11us/20050715Pm01B1/detail.html .

Beaucedine Glacier:
Living Statue		37 - 39
Lugat			39 - 42
Bat Eye			40 - 42
Goblin Poacher		40 - 43
Goblin Robber		40 - 43
Goblin Reaper		40 - 43
Cold Gigas		40 - 43
Sleet Gigas		40 - 43
Snow Gigas		40 - 43
Stone Golem		40 - 42
Ice Elemental		44 - 46
Dark Elemental		44 - 46
(I recommend avoiding Ghasts, Lugats, Goblin Traders, Rime Gigas, Bat Eyes, 
and the elementals)
(Ghasts and Lugats may sleep you)
(This whole region can be a pain.  Too many mobs to avoid or be careful of)

Behemoth's Dominion:
Lesser Gaylas		40 - 42
Greater Gayla		42 - 44
Demonic Weapon		45 - 46
Demonic Weapon		45 - 46
Lost Soul		45 - 47
Master Coeurl		45 - 50
Bhuta			46 - 48
Thunder Elemental 	48 - 50
Light Elemental 	48 - 50
(I recommend avoiding Bhuta, the elementals, and Master Coeurls)
(Bhuta and Lost Souls may sleep you)

Yhoator Jungle:
Young Opo-opo		40 - 44
Goblin Digger		41 - 44
Goblin Reaper		41 - 45
Worker Crawler		43 - 46
Goblin Robber		45 - 49
Goblin Poacher		45 - 49
Goblin Trader		45 - 49
Master Coeurl		47 - 50
(I recommend avoiding Young Opo-Opo, Tonberries, and Master Coeurls)

Sanctuary of Zi'Tah:
Goobbue Gardener	40 - 43
Ogrefly			41 - 44
Goblin Poacher		42 - 46
Goblin Robber		42 - 46
Goblin Reaper		42 - 46
Master Coeurl		44 - 47
Hell Hound		46 - 50
Rock Golem		49 - 50
Rot Prowler		49 - 53
Lost Soul		51 - 55
(I recommend avoiding Master Coeurls and Hell Hounds)
(Lost Souls may sleep you)

Altepa Eastern Desert:
Desert Dhalmel		39 - 44
Doom Scorpion		44 - 47
Antican Decurio		44 - 49
Antican Sagittarius	44 - 49
Antican Speculator	44 - 49
Lost Soul		44 - 48
Goblin Poacher		45 - 49
Goblin Robber		45 - 49
Goblin Reaper		45 - 49
Goblin Digger		45 - 49
Lesser Manticore	47 - 49
Diatryma		47 - 50
(Antican Speculator and some Lost Souls may sleep you)

Altepa Western Desert:
Desert Spider		40 - 44
Antican Essedarius	41 - 45
Desert Worm		43 - 47
Desert Dhalmel		44 - 48
Antican Retiarius	45 - 49
Antican Eques		45 - 49
Desert Beetle		47 - 51
Lich			49 - 53
Fallen Knight		50 - 54
(I recommend avoiding Cactuars)
(Antican Retiariuses and Liches may sleep you)

Xarcabard:
Lost Soul		42 - 45
Cursed Weapon		43 - 45
Evil Eye		45 - 48
Graupel Gigas		45 - 48
Hail Gigas		45 - 48
Blizzard Gigas		45 - 48
Demon Pawn		48 - 52
Demon Wizard		48 - 52
Demon Knight		48 - 52
Ice Elemental		48 - 50
Dark Elemental		48 - 50
Shadow Dragon		52 - 53
(I recommend avoiding elementals, Etemmu, Frost Gigas, Evil Eyes, and Demon
Warlocks)
(Lost Souls, Cursed Weapons, and Demon Wizards may sleep you)

Yhoator Jungle:
Anemone			51 - 54
Goblin Hunter		51 - 55
Goblin Bouncer		51 - 55
Puroboros		51 - 54
Water Elemental		53 - 55
Fire Elemental		53 - 55
(I recommend avoiding Anemone and elementals)

Altepa Western Desert:
Goblin Digger		51 - 54
Goblin Enchanter 	51 - 55
Goblin Hunter		51 - 55
Goblin Bouncer		51 - 55
Goblin Welldigger 	51 - 55
Tulwar Scorpion 	53 - 56
Desert Manticore 	53 - 57
Antican Hoplomachus 	54 - 58
Antican Lanista 	54 - 58
Antican Secutor 	54 - 58
Phorusrhacos		57 - 60
(Antican Lanista may sleep you)

Uleguerand Range:
Glacier Eater		58 - 62
Variable Hare		58 - 61
Cwn Annwn		59 - 64
Esbat			59 - 62
Uleguerand Tiger	59 - 62
(I recommend avoiding Cwn Annwn if possible)

Ro'Maeve:
Killing Weapon		60 - 64
Ominous Weapon		61 - 63
Cursed Puppet		65 - 69
Magic Flagon		68 - 70
Mythril Golem		69 - 70
(Ominous Weapon may sleep you)

Attohwa Chasm:
Pit Antlion		49 - 51
Tulwar Scorpion		58 - 59
Lich			62 - 64
Mummy			62 - 64
Monarch Ogrefly		64 - 65
Sand Lizard		65 - 67
Corse			66 - 67
(Lich may sleep you)

Cape Teriggan:
Beach Bunny		62 - 65
Sand Lizard		62 - 66
Robber Crab		64 - 67

Valley of Sorrows:
Velociraptor		66 - 69
Peryton			69 - 72
Valley Manticore	72 - 74

Bibiki Bay:
Tragopan		71 - 73
Hobgoblin Martialist	72 - 75
Hobgoblin Fascinator	73 - 75
Hobgoblin Venerer	73 - 76
Tropical Rarab		73 - 76
Hobgoblin Alastor	76 - 79
Hobgoblin Physician	76 - 78
Hobgoblin Toreador	76 - 79
Tartarus Eft		76 - 78
Hobgoblin Blagger	77 - 79
Catoblepas		78 - 80
Hobgoblin Angler	80 - 80
(I recommend avoiding Teine Sith)
(Hobgoblin Fascinator, Hobgoblin Alastor, and Hobgoblin Toreador may sleep you)