Kerning City Pqing is a very good option at level 21, although you may just waste your time if you miss pqes. Also, at the lower levels (21-24) people don't usually pick you for a Pq. Another good place to train is the Pig Beach. A precaution there is extremely fast respawn and the pigs may mob archers. Another thing to be careful about is the random spawning Iron Hog which will probably kill you.
If you happen to find one just change channel. Another good option for levels 20-25 is the Ellinia tree dungeons. Horned Mushrooms drop pretty good maple story mesos and the the Green and Horned Mushrooms will both give you good experience. You will also get a chance to get a pan lid which for archers is worthless, so you can sell it for extra mesos. A good place with exotic kinds of mushrooms are the Mushroom Park in Zipangu, which are a great option at this level since you should be OHKO (One Hit Knock Out) the mushrooms.
Level 25-30The second job advancement is getting closer all the time! If you are in need of mesos, a good option is the orbis towers fighting jr.sentinels. They drop good money and you can also get bronze arrows from them. One of the best area is the Ant Tunnel. With extremely fast respawn and good experience, you can level up fast. Also, during the Mapel Birthday event, simply training there can gain you a Maple Hat or maple story mesos. The Ellinia Tree Dungeons and the Mushroom park in Zipangu are stilll a good option. By these levels people should be scrambling for you in Kpq's so joining a pq is a good option, altough you are still wasting your time if you miss.