First things first

Read the mod's instructions. ALL OF IT. Bothering with anyone who has ignored the instructions is an utter and complete waste of time. Make sure you have the required mods installed, ALL OF THEM, and make sure your minecraft worked with those installed.

Just because your minecraft reaches the menu screen doesn't mean it works. Create a new World, run around a few steps, mine a Block. If it hasn't crashed yet, you probably did not mess up.

Common mistakes resulting in blackscreens

Did you mess up installing forge or have old mods installed? DID IT WORK BEFORE?

In case of new Minecraft version, delete the following folders (if present): mods, config, buildcraft, redpower. These folders may contain outdated files being loaded still, and crashing.

Did you make sure you have the correct version of Forge, and other requirements? Redownload the latest ones if you are unsure.

If in doubt, always start with a fresh minecraft setup.

I'm getting a black screen and i followed all instructions?! What now?

Fetch the ForgeModLoader-client-0.log from your minecraft directory and present it to someone who can read logfiles, like, in the forum.

Before you run off and spam the board with your logfile on pastebin, take the time to READ IT. The crash reason is usually stated in more or less clear english and if it's something obvious you might not need help to fix it.

Also check the mods forum thread, at least the last 2-3 pages. Someone had your issue before you, i guarantee it.

Mod Specific Issues

Dynamic Lights: Nothing sheds light. Read the installation instructions included in the download.

Minions: No Deeds. Read the installation instructions included in the download.

Ruins: Nothing spawns. Read the installation instructions included in the download.