Training locations for Dagger Rogues

* Level 10-15: Oh wow, look at those slimes, they're so overjoyed, they're bouncing with happiness! Well, that can't be right, so let's terminate their happiness (and their lives) with your speedy knife of death, and the best place to do so is the Slime Tree (not tree dungeon). I don't suggest you to spam Double Stab here as it won't be necessary, unless you feel like throwing money into the wind or something. Henesys Party Quest is a good option.

* Level 16-19: All you rich bandits can now unleash stabbity death upon pigs now, so go do so at Pig Beach. While their poorer brethrens can also train there, you won't make much profit, so stay at slimes. Mushroom Garden is also a very good training area.

* Level 20-23: Now, all bandits, rich or poor, can enjoy the shower of sun rays (containing hazardous UV radiation) at Pig Beach also you can start party questing at kerning, but I suggest not to start that until around level 24. Double Stab spamming bandits will find their 1HKO rate much higher with a better weapon, and for you poorer bandits... if you just found that Dankke that you sold to an NPC for 50000 mesos, you can start doing stabbity death for a while too.

* Level 24-29: At this point, all bandits should have maxed Double Stab. If you want you can start party questing in kerning, as you are level 24 which is a good level for party quest in kerning. Or if your wallet is happy enough, go murder green mushrooms with Double Stab (and perhaps some follow up normal attacks), and pray to Maple God a pan lid drops. If your wallet is mad at you, either ignore it partially and go normal attack frenzy with Green Mushrooms, or treat it with a few days at Jr Sentinels (which drops 60-90 meso per kill!), which will surely make it happy.
http://strategywiki.org/wiki/MapleStory/Thief_Guide