Yes, I know, there's already tutorials on this: however I encountered problems with versions; moreover, one tutorial is for installing mod X, another for installing mod Y, etc.

Spoiler: Very brief explanation

The main reason why I encountered problems when I was a noob at installing mods, is because most mods can't be installed alone, but require some particular mod loader under which they can work. Moreover, there's two main different mod loaders for MC: Forge and Liteloader; if you want to install some mod(s) requiring the former and some other mod(s) requiring the latter, you have to install both Forge and Liteloader, and you gotta install them so that the latter doesn't override the former: otherwise you will get only the mods running under the latter.

So here I am: writing a single tutorial for all the useful and legal mods on ECC, with dependencies and shit. If you're not interested in a particular mod, just skip that step.
Here follows a list of all the useful, legal and working mods running on MC 1.12.2 (and a brief explanation on each one):

Spoiler: THE list

• OptiFine
  
  Spoiler: what's it for

  Better and faster graphics, mainly.
• JourneyMap
  
  Spoiler: what's it for

  Shows a very useful mini-map in one corner of your screen.
• WorldEdit (singleplayer)
  
  Spoiler: what's it for

  Can't do much with it on ECC server, however it's extremely useful when building huge projects in singleplayer creative; on top of that, you can save a .schematic file of what you've built and then load it with Schematica on ECC server.
• Schematica + LunatriusCore
  
  Spoiler: what's it for

  Schematica allows you to load a .schematic file, even while playing on ECC server, and superimposes it on your view, making it much much faster to manually build on ECC something that you've already semi-automatically designed and built in singleplayer creative (or even .schematic files made and given to you by other users), allowing you to do it a ton times faster. LunatriusCore is only needed to have Schematica work (it's also needed for other mods which I haven't tested yet and which are therefore not present in this list).
• MacroMod
  
  Spoiler: what's it for

  This is the mother of all mods and I can't really explain it in a few lines. You want this mod, and you want to learn how to use it. It'll prove very, very worth the time you spent learning on it. There's tons of tutorials and projects on this forum making use of it: @314 made a whole compilation of macros which complement each other, check it out (I've been planning of doing the same since a long time but never found the time, so PMC is the only such a thing I know of on ECC as of today).
• TabbyChat + MnmUtils
  
  Spoiler: what's it for

  TabbyChat splits your chat into different tabs according to users and channels. Among other reasons why to install it, it's extremely useful to avoid missing messages. MnmUtils is only needed to have TabbyChat work.
• WorldEditCui
  
  Spoiler: what's it for

  If you installed WorldEdit, you want to install this as well (unless you want to waste whole hours of you time scratching your head for not seeing what you're doing).
• Gammabright
  
  Spoiler: what's it for

  Allows you to see in the dark. If you have /nightvision you don't strictly need it, however Gammabright is better because: 1) if you turn it on, it stays on even if you change world and you don't have to type /nv (or even bind it to some event) every time you go back and forth, 2) it gives you a much better view underwater, 3) it doesn't show that obnoxious particle status effect.
• PopEnchantTagsRevived
  
  Spoiler: what's it for

  Shows the enchants on a tool while scrolling over it on the toolbar, with no need to open your inventory and hover on it. It's not necessary if you named all your tools in a smart way, but why not have it in any case.

I will update the thread as soon as the new mods are released for new MC versions.
This tutorial works fine on Linux, but it should work on other systems as well, being that MC runs on Java.

If you download the correct version of everything and you don't encounter obstacles, you should get a working environment in less than 15 minutes (including downloads). I don't guarantee this will possibly work with the MC versions yet to come, but you can always try.

Let's get started!


Prerequisites:

• Latest JRE installed and working (currently Oracle Version 8 Update 161).
  • Check your version here: https://www.java.com/verify/
• Latest vanilla MC installed and working.
  • If you have (working) custom profile options, copy them on notepad (you will need to paste them more than once).
• Latest SquidHQ launcher downloaded and working (currently S0.0.3).
• I assume that you know what Operating System (GNU/Linux, macOS, Windows, other) you're running and where your MineCraft main directory is.

Dependencies

• The following mods depend on Forge and require that you install it first:
  • Optifine
  • JourneyMap
  • WorldEdit (singleplayer)
  • Schematica + LunatriusCore
• The following mods depend on LiteLoader and require that you install it first:
  • MacroMod
  • TabbyChat + MnmUtils
  • WorldEditCui
  • Gammabright
  • PopEnchantTagsRevived

Procedure

Spoiler: If you want one or more mods dependent on Forge:

Spoiler: Install Forge:

1. Download recommended Forge installer for MC 1.12.2 (currently 14.23.2.2611) according to your OS.
2. Run Forge installer.
3. Launch MC!
4. Set up your custom profile options (if any) for the new profile just created.
5. Test that everything works fine.

Spoiler: Install Optifine:

1. Download latest OptiFine for MC 1.12.2 (currently 1.12.2_HD_U_D1).
   
2. Place the .jar file in the [mods/1.12.2] directory.
   
3. Launch MC!
4. Test that everything works fine.

Spoiler: Install JourneyMap:

1. Download latest JourneyMap for MC 1.12.2 (currently 5.5.2).
2. Place the .jar file in the [mods/1.12.2] directory.
3. Launch MC!
   
4. Test that everything works fine.
5. Very important: follow these instructions if you don't want to be banned!

Spoiler: Install WorldEdit (singleplayer):

1. Download latest WorldEdit for MC 1.12 (currently 6.1.8 - no worries, WorldEdit for 1.12 is still compatible with 1.12.2).
2. Place the .jar file in the [mods/1.12.2] directory.
3. Launch MC!
4. Test that everything works fine.

Spoiler: Install Schematica + LunatriusCore:

1. Download latest Schematica for MC 1.12.2 (currently 1.8.0.168-universal).
2. Download latest LunatriusCore for MC 1.12.2 (currently 1.2.0.42-universal).
   
3. Place the .jar files in the [mods/1.12.2] directory.
4. Launch MC!
5. Test that everything works fine.

Spoiler: If you want one or more mods dependent on LiteLoader:

Spoiler: Install LiteLoader:

1. Download latest LiteLoader installer for MC 1.12.2 (currently 1.12.2 #4) according to you OS.
2. Run LiteLoader installer.
3. Very important: if you previously installed Forge, then select extend from the Forge profile (the one you just created when installing Forge).
4. Launch MC!
   
5. Set up your custom profile options (if any) for the new profile just created.
6. Test that everything works fine.

Spoiler: Install MacroMod:

1. Download latest MacroMod for MC 1.12.1 (currently 0.15.4 - no worries, MacroMod for 1.12.1 is still compatible with 1.12.2)
2. Place the .litemod file in the [mods/1.12.2] directory.
3. Launch MC!
4. Test that everything works fine.

Spoiler: Install TabbyChat + MnmUtils:

1. Download latest TabbyChat for MC 1.12.2 (currently 2.3.4).
2. Download latest MnmUtils for MC 1.12 (currently 1.3.1 — yes, it's for 1.11.2 but it still works).
3. Place the .litemod files in the [mods/1.12.2] directory.
4. Launch MC!
5. Test that everything works fine.

Spoiler: Install WorldEditCui:

1. Download latest WorldEditCui for MC 1.12.1 (currently 1.12.1_01 - no worries, WorldEditCui for 1.12.1 is still compatible with 1.12.2).
2. Place the .litemod file in the [mods/1.12.2] directory.
3. Launch MC!
4. Test that everything works fine.

Spoiler: Install Gammabright:

1. Download latest Gammabright for MC 1.12.1 (currently 3.7 for 1.12.1).
2. Place the .litemod file in the [mods/1.12.1] directory.
3. Launch MC!
4. Test that everything works fine.

Spoiler: Install PopEnchantTagsRevived:

1. Download latest PopEnchantTagsRevived for MC 1.12.2 (currently 1.2.0 for 1.12.r2).
2. Place the .litemod file in the [mods/1.12.2] directory.
3. Launch MC!
4. Test that everything works fine.

If you encounter any problem, let me know exactly where you got stuck and I'll do my best to help you (which is not a lot, but hey).


F.A.Q.

• What are your custom profile options?
  • Here's the ones I use, but of course you might need to tweak them a bit, depending on your system:
    Code:

    -Xmx3G -Xms3G -Xmn512M -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -server -d64

  • I should probably change something, but I'm too lazy to do tests.

Enjoy!

 

Could a Mod please change the title to:

Thank you :)

 

How did you install OptiFine without Forge? I couldn't find a Forge-independend installer

 

Added support for JourneyMap!

Could a mod please change the title to "How to install OptiFine + JourneyMap + MacroMod + TabbyChat on 1.10.2 (yet another tutorial)"?

 

Sure! However I'm not sure what this "fail" means:

does it mean that you don't get the instability error message, or that you did get it again?

 

I see. Well, according to this comment:

you don't really need Forge, as it's not needed for OptiFine and you don't want JourneyMap.
Now;I didn't test this myself but, according to what I found doing a quick search, there's no specifically forge-independent version (the one I looked for — see my comment below Video's) just because you don't technically need Forge for the one and only version of OptiFine you can download!
So here's what you have to do if you don't want/have Forge: instead of placing OptiFine's .jar file in the mod directory, you just run that .jar file instead, and it will install OptiFine independently of Forge. (if you put a copy of OptiFine's .jar file in the mod directory during your earlier attempts, remove it, just in case)
Then, when you install LiteLoader, instead of chaining it to Forge's version you have to chain it to OptiFine's. The rest should be the same.
Try and let me know :)

 

@Videowiz92 as you will probably be alerted in any case due to my quote: could you please change the title to "How to install OptiFine + JourneyMap + MacroMod + TabbyChat on 1.10.2 (yet another tutorial)"? Thanks :)

 

Updatet to OptiFine 1.10.2_HD_U_C3!
Could a Mod please change the title? A reference to JourneyMap is still missing, the new title should be:

Thanks :)

 

Updated to 1.11.2: unfortunately tabbychat was unavailable, I'll add it as soon as I notice an update.
Could a mod please change the title of this thread to: "How to install OptiFine + JourneyMap + MacroMod + TabbyChat (yet another tutorial)"?

 

Ugh. I'll update it as soon as I'm home with a decent connection

 

Updated with:

• TabbyChat support (whoooo!)
• no version-specific links anymore: I couldn't realistically keep them all up-to-date, and it's pretty easy to find the latest one
• no OS-specific links anymore: same reason as above.

 

Windows is Evil, Mojang's launcher is Evil, are you trying to poison me with a double dose?