You guys gotta start giving us some help, so that we can help you.
Example: It's extremely hard to guess what kinda gears you have, what level you are, and what class you are.
Making zeny heavily depends on class, Level, and equips. So Without that, all we can do is spitball.
1) Skellington. Also called "Niff" by people.
Most popular, and most crowded of all the leveling places, to be sure.
Loots are good, the monsters are fairly weak, and the mobs are increased on this map.
The most profitable idea would be to aquire a DBSS Mace, and use a Blacksmith/Whitesmith.
Due to the [Greed] Skill, you can pick up the loots from the monsters you kill easily.
You could also use a highpriest, but they don't make close to the same amount, unless you have a BS/WS tag along with you.
Which in the begining, can be more profitable then trying to solo the whole time.
The downside to this is: It's way too freaking crowded. You can bairly mob anymore.
2) Hunt SQI items/Farm Cake. (Alot of maps/Toyfactory 2)
It won't net you the same amount of Zeny as Skellington will, but it's considerably easier, and doesn't require any gear.
It's much easier for a newer player to do. You can hunt Red bloods, and sell them for 4K+ Each.
Cakes go for about 3.5K each, or more on War of Emperium days. Sell them in Pront, Alberta, or a popular town that's home to some non-trans guild.
(non trans guilds tend to use Cake more often then Trans guilds, who usually use Slim White potions)
3) Start a Leeching business. (Skellington/LH3)
There are two popular places to leech, both of which have two desgnated classes that are "Best" at each job.
First is the Skellington, or Nif leech. These run for about 1mill each/hour or so. They are usually done by a Highpriest.
The second is LH3. The only two classes that can leech efficiently up here are Creators and Champs.
Creators however, will very rarely leech, since it costs so much for them to kill things.
Most often it is 1.5-2mill per session + x amount of Grapejuice, and the lenght of the session depends on when they run out of GJ.