If you have a party, you should attempt Huike's quest and obtain Huike's Letter so you can get a free Monk later. The enemies in the Shadow Trigram also drop Shield of Protection books which are worth quite a bit of money. The problem is you WILL get mobbed so be prepared for it.

At level 20 you get a free 7 day license package. Use this before you reach level 25 otherwise it goes to waste.

Level 24-32 (Angkor Wat):

This will be your first encounter with some tough enemies. If you know how to fight them, they're easy. The flying Evil Monks can only be hit by projectiles or skills. They also have a powerful poison skill. A Monk's Holy Guard can cure it but a lot of atlantica gold players will not have one yet. The second set of enemies here are just as powerful. These are the ogres. The White Ogre are weak against skills but strong against physical attacks. If you have Swordsman, 2 level 20 Flame Swords will kill a White Ogre. The only good spot to train here are at the Moss and Sorcerer Golems. The Sorcerer Golems will cast a weak heal on any hurt enemy making them waste their turn. The Moss Golems are the only ones who will seriously attack and they are weak. They can come in large groups if you're not careful, but if you can hit multiple targets with axes or guns, they will barely attack you.

Level 32-40 (Insect Nest):

At level 30 there is a side quest to kill the Night Fox. Its good if you are in a party because the mobs tend to come in sets of 2. Its great experience and chances are you will need to grind a bit before you can activate the Insect Nest quest chain. Most of the mobs in the Insect Nest also comes in a group. Keep in mind that flying enemies and the Worker Ants are immune to cannon fire so you have to rely on skills. At this point level 35 equipment starts to drop in the form of Insect Equipment Box. I recommend you upgrade level 25 armor using Enchant Stone [Beg] because level 35 equipment is expensive and Enchant Stone [Int] is even more expensive and not worth investing into at this point. A +4 level 25 set will last you until level 50. Try to get +3 Asura weapons if you can as well. The best spot to train is at the Worker Ants in the beginning. The Tarantulas and Hell Spiders are not bad if you can kill Hell Spiders in 1 turn. If not they will Deadly Shot you into oblivion so if you attack them make sure you can kill them. You need to stay until level 40 when you can continue to the next dungeon.