Lots of minecraft servers have a plugin that adds currency, and this can be used to buy almost anything on the server, whether the currency is called an mc-buck or a Euro. Because of it's usefulness, everyone wants a lot of it, no? Maybe there's something you want to buy on a server, or maybe you want to rub into your enemies' faces that you're the richest on the server. Here are some ways to get some in-game money.

1. Make a farm. Keep what you and maybe your friends need, then sell off the rest. Lots of people on minecraft don't have a farm and need food (who doesn't), so if you can't sell food to the official server shop, most likely there are lots of players wanting some food. Nether warts are pretty rare and pretty useful for making potions (most potions need at least one). Because of this, you can probably make more cash if you have a nether wart farm, rather than a normal farm that has potatoes, carrots ect. So I say, get some soul sand (the one block nether warts grow on), some warts, and build a farm! Btw, you might want to make a farm that needs merely the push of a button to harvest everything. I understand the concept and could even make one, but idk really how to explain it. If you want to learn more, I suggest you search youtube with these words: "automatic minecraft farm".
   
   
2. Make a cobble/obsidian farm. Cobblestone can be used for crafting, or for making a home that will be a challenge for a griefer who doesn't have very much yet. Besides, cobble plain looks cool and medieval. All you need for a cobble farm is a bucket of water, a bucket of lava, and something to build with other than wood. If you want to make one of these, make sure you have A: someone to buy the cobble, B: a shop to sell it to, or C: some way you can use it yourself. To make a cobble farm, simply build a one block high and one block wide row of blocks that's four blocks long. Make another like it one block away yet parallel. At each end, connect the two rows, whatever you want to call them. In each end goes either water or lava. When they meet, it's cobble ho! Mine the cobble, and more will appear! For an obsidian farm, build a three by three square with no middle. Build it up another block. Put some lava on the bottom of the center (lava HAS to be on the bottom), then water on top. Collect the water, then mine the obsidian.
   
   
3. Find a shop loophole. You really should look for a loophole at the server shop or at a player's shop. Maybe you can buy bones cheap and sell bone meal for good cash, or maybe you can buy sand for a few bucks and sell it somewhere for a few bucks more than you payed. That's how I got rich on macstercraft (but I spent that fortune).
   
   
4. Raid. If you're on a factions, a.k.a. raiding server, simply raid other factions. Make a faction, go at least two thousand blocks away from spawn, claim a patch of land with /f claim , then build the best base you can as fast as you can. Don't let into your faction anyone you either don't know, or haven't observed for a while. Maybe you want to make an under ground base, or maybe you want to build a tower to the sky, build out from it, then destroy the tower therefore making a sky base. Whatever you want, just make it as anti-grief as possible. When you have a fairly safe base with plenty of chests, search for other factions' bases. When you find land owned by one, do /f f (the Fac's name) and check their faction power. If it's more than yours, you can't raid them. If it's less, do /f claim and start destroying and stealing from chests! Some people on faction servers don't even bother claiming the land they build on! You can then sell what you get to get in-game money.
   
5. Grief. I suggest that you first check to see if griefing is allowed on the server you might do it on, then make your choice. Getting rich from griefing should be a last resort, unless your victims all deserve it. You can sell what you get, but beware, you may get kicked, temporarily banned, or even permanently banned from a server for griefing. BEWARE!!!
   

I hope this helped, and please give me a diamond if you liked this. Good day to you!