Guide By [GM] Kakashi of nwro
Lv 1-12: Leveling as a novice. Stick to low level monsters like Porings, Pupas, and Roda Frogs. If being tanked then try Poporings.
Lv 12-30: The first few jobs as an Acolyte will be on the same monsters killed as a novice, or one can also move to Payon Caves instead of killing Poporings. Unless the Acolyte has good SP/INT gear or friends then their SP will run out fast when heal bombing, so they have to make sure that they have an equip like a Mace to defend themselves while regenerating HP and SP.
Lv 30-40: Here is where one can choose to solo or to jump right into fully supporting a party. The Acolyte can choose to heal bomb monsters in the 2nd and 3rd levels of Payon Caves, or possibly heal bomb at the Glastheim Church Yard, but the Mimics, Hunter Flies, and Dark Lord make this challenging. The easiest thing to do is to find a low level Mage to party with, either at Prontera Argiopes, Louyang Mi Gaos, or Clock Tower or Glastheim Sewer Stings if both party members have good equipment.
Lv 40-50: Continue heal bombing at the aforementioned places, and possibly move to Glastheim Prison once you get Holy Light to kill Zombie Prisoners and Injustices. Also may continue leveling with Mages, but try to be at Clock Tower and Stings now unless the party members are all new to RO.
Lv 50-65: Again mostly the same places, try to only party now as soloing gets pretty slow and dull. May want to step it up a bit and find a newly changed Wizard to level with at Prison instead since they can mob. Or a low level Dancer/Bard to go to Stings with since they'll kill much more efficiently than a Mage. Also, if the Acolyte has very good equipment they can consider partying with a Grand Cross Crusader at Glastheim Chivalry.
Full Support Priest / Solo
Payon Cave 1 Skeletons and Zombies: 12-30
Tatami Maze Firelock Soldiers: 30-66 (Pneuma highly suggested)
Glast Heim Churchyard Everything in sight: 50-70
Sphinx B4F Anubis: 70-99 (Turn Undead highly suggested)
Louyang Field 1 Mi Gaos: 30-70
Norgroad Everything in sight: 70-99
Ice Dungeon 3 Everything in sight: 80-99
Ice Dungeon 2 Everything in sight: 95-99
Somatology Laboratory 3 Everything in sight: 95-99
Sphinx B4F Anubis: 70-99 (Grand Cross Crusader highly suggested)
First of all, it's a good idea to level all your basic skills at Training Grounds. An aco should not be afraid to spam his nove potions, as they will turn to weak once you job change to your first job.
Second, Battle acos are some of the hardest classes to level. It's a requirement to reach Job level 50, and Acos have to use 20 skill points in Divine Protection and Demon Bane just to get their first Monk Skill. Besides, they have no offensive attacks at their disposals.
Prontera Culvert Tarous and Plankton: 10-20
From level 10 and up, try fighting Tarous and planktons at Culvert level 2. He should watch out for familiars. Bringing some red pots will help him greatly in the first levels. Level his heal up to level 3, then get Inc. Agi 1 for the walking speed.
Mt. Mjolnir Horns: 20-30
If he sits upon a large pile of money, buy a good amount of red potions and try taking down Horns one map north for the Culvert entrance. Those and Cocos will do good Exp the next ten levels. If he's averagely rich, get him a Stunner for 60k in SW Morroc. He can use it after level 27, and he'll notice a significant difference in ATK. If he's not very rich, try going some more for Tarous. It's slow, but that's the life of a Battle Aco. During this stage, try to level his Pneuma tree. (Ruwach 1> Teleport 2> Warp Portal 4> Pneuma 1)
Mt. Mjolnir Horns,Toy Monitoring Room Cruisers: 30-40
By now, he should be able to rely more on his heal than his pots. If he wants to, he can slow level some on Horns before getting to the real deal: Long ranged enemies. Pneuma is a skill which grants him complete defence against long ranged attacks, such as gunshots from Firelocks or Cruisers, arrows from Gargoyle or Archer Skeleton etc. For leveling Solo, this is one of the most usefull skills. If he has proper Dex, he can start leveling some great levels at Cruisers.
By the way, BEFORE HE REACHES LEVEL 40, he should reconsider his skill points. If he's not pleased with them, he should go to the Hypnotist close to the Tool Shop in Pront and have them reset. After level 40, he can't do this anymore.
Tatami Maze Firelock Soldiers, Toy Monitoring Room Cruisers: 40-50
Either stay at Toy Factory for ten levels more, or head to Alberta, and go to a place called Amatsu, and enter the dungeon after completing the dungeon quest. Find an enemy called Firelock Soldier there. These guys are great Exp, and the cards they drop are worth very much. Remember, pneuma doesn't ward off skills. Firelocks have a fire attack which can deal about 7-800 damage. Also, getting to Amatsu costs 10,000z.
Carry a hiding clip/nile rose/belt to hide when come across Shinobi.
Tatami Maze Firelock Soldiers,Toy Monitoring Room Cruisers: 50-60. Whatever works best. Firelocks give better JEXP. Cruisers = Safe, Firelocks = Best.
Tatami Maze Firelock Soldiers: 60-Job change
Firelocks, firelocks and more firelocks until Job 50. Leaf Cats is also a good place once after Base Level 60.
Juno Field Sleepers, Morroc Field Sandman or Tatami Maze Firelock Soldiers: Job Change - 75
Basically, it's firelock soldiers until the player gets enough job levels. If the player chooses to be an occult impact monk, the player should go to Sleepers once the player gets lvl 5 Occult Impaction. If the player is an AGI type monk or just wants to go hand-to-hand combat with monsters for leveling, they should go for sandman.
Freezer, Permeter, Solider: ~75+ Perfect for Occult Impact Monks. You need a Triple Clamorous Chain and Priest with Lex Aeterna and you can one-hit the turtles. Great EXP also for the higher monks. Only the Pests could get on your nerves ;)
Hill Wind: 70-85 to Combo Monks with a earth element weapon and 190 flee rate. The hill winds have low HP and a good among of exp and job exp. Just watch out of Drosera's Close Confine.