What would be helpful for newbies to know before getting started?

edit

First I'll try to elaborate a bit on the already mentioned points:

1. Basic Linux and especially Ubuntu
   • Getting used to using the windows and workspaces relevant shortcuts (in Unity, hold SUPER/WINDOWS)
   • Knowing what apt-get does and how it works
   • Knowing how to set up ssh connections using keys
2. Using the terminal
   • Getting familiar with TAB completion and history
   • Know the basic shortcuts CTRL+C, CTRL+ALT+T, CTRL+SHIFT+T, CTRL+(+|-|0)

What also helped me:

1. Having a basic knowledge of threads and their hazards (especially relevant for C++)
2. Getting familiar with version control systems and their underlying concepts
   • git, subversion and mercurial are all used in ROS repositories
   • Focus on one and use it for your projects (git works best for me)