The answers to this cross-platform related question are useful, however I want my (C++) game to run on Windows and Linux (and be packaged for Ubuntu) only. I'm not interested in platforms like mobile or consoles.
Are there any specific tips or suggestions for this case?
Also, if I get the game to work on linux, is it difficult to add support for OSX?
Updating with more information:
It will be a 3D game simulating the motion of spacecraft in the solar system. We will use Ogre3D for the graphics. We're still in the design phase, so there's no code written yet.