Limit RO is blessed with active market, meaning, not only people selling stuffs but they also buy stuffs from farmers, mainly food ingredients. This helps a lot because players can have options on what they want to farm, not just items to sell to NPC. Here are some suggestions on where to farm, who to kill and what to loot:
Moscovia Dungeon 3
This one is quiet popular for newbies since it doesn't require you to have certain set of gears to hunt in this map. Mavka drops Crystal Mirrors and Witherless Rose make sure to loot them but if you want to get extra coins, you can loot Blue Herb from her too.
Ice Dungeon 3
Gazeti drops Ice Piece and Iceicles drop Ice Crystal, there's huge demand of these items in Vending Harbor. Make sure you use wind element to make it easier to kill these mobs.
Veins Field 2 & 3
Drosera Tentacles from Drosera is also very popular food ingredient and it's pretty easy to kill Drosera since, you know, they don't move.
Glast Heim Underground Cave 2
Beef Head from Majoruros is not as popular as the ingredients I mentioned above but some people still buy them occasionally, also you can loot White Herb, Lemon and Oridecon here!
Orc Dungeon 1 & 2
You will need a Wraith card (accessory) so those undead monsters will have chance to drop Giggling Box, the most popular healing item in Limit RO.
Thanatos Tower 9, 10 & 11
100% autoloot is a must! You can sell everything you get here to NPC, especially Stone of Sage. The downside of this method is you need a Ranger with at least White Wing set and +4 Big Crossbow with Archer Skeleton cards or Huterfly cards so... Not that suitable for newbie.
Hilmir's note: There are more farming places with good loots but those I mentioned above are what I personally used or at least tried before.
If you're not the kind of person that enjoy farming for hours and prefer to do instances, you can make an army of either Ranger, Bishop or Sorcerer on your account so you can do certain instances more than once a day (OGH, ET, Faceworm, etc). Having them in 1 job will save a lot of time and resources since you will only need 1 set of equipment.