Angus,
Simply click options before you login to Minecraft. Select for the game to "Force Update"
This will refresh your game to the latest update, with everything on default.
THIS IS YOUR CANVAS!
Make sure every mod you attempt to install has every prerequisite installed and instructions are followed when you do. (MAKE SURE THEY'RE CURRENT WITH LATEST VERSION)
You should not receive crashes unless the mod is not compatible with Minecraft, in which case, you're out of luck.
