Before submitting your crash report or bug report for help on the forums, It's sometimes best to try and solve it yourself

Not trying to often ends up with duplicate threads from different users all about the same issue and ending up in taking up forum space.

This thread will be a guide on some really common issues that you may encounter with any mods in general, not just the DM or any other SWD mods.

java.lang.OutOfMemoryError: 

Your Minecraft doesn't have enough memory to do what you're trying to get it to do, usually the way to sort this is..you guessed it...give it more

You can do this by following the below steps:

If your Minecraft freezes during loading forge and never makes it to the main menu, then head over to your .minecraft folder and into the config folder (.minecraft/config) and open splash.properties in notepad or whatever text editor and change the line enabled from true to false like so:

Show content

Then save and launch your game as normal.

java.lang.IndexOutOfBoundsException
at java.nio.Buffer.checkIndex
at java.nio.DirectIntBufferU.get
at net.minecraft.client.renderer.RenderGlobal...

You're playing 1.7.10...with 1.8+ settings....Lower your render distance.

These libraries failed to download. Try again. org.scala-lang:scala-library:2.10.2, org.scala-lang:scala-compiler:2.10.2
Download this: https://bitbucket.org/luacs1998/forgelibrarydownloads/downloads/fmllibs16.zip and extract it to your .minecraft folder, then try running Minecraft, or redownload the installer.

java.lang.NoClassDefFoundException: net/minecraft/client/something :

One of your mods is client only and you're on a dedicated server (Or vice versa!). Check which ones, and remove them

If your main menu background is compressed to a corner, and the rest of the menu is black/white: Update your Forge to at least 10.13.1.1226 or add -Dforge.forceNoStencil=true to the VM arguments in the launcher.

Invalid Session (Restart your game):

Well this is kinda obvious isn't it?

If you're using the Technic launcher, you must log OUT of it and back in, you MAY have to do the same with the normal launcher too

"You need to run the version X manually once."

Another obvious one...

This means that you have to run VANILLA minecraft (no mods) for the version listed before you can install Forge.

I'm leaving this thread open for people to suggest fixes for other issues they have encountered in the past. This is NOT a place for you to reply with, with your crash report, please do that in a new thread if this one did not help you.