Okay, sometimes you can't find a partner to play, or you just want some practice.
So, all you need is a six sided die.
The only time you need to use it is when you use your dial to assign a warlord:-
5 planets - re roll on a 6
4 planets - re roll on a 5 or 6
3 planets - 1 or 2 = planet 1, 3 or 4 = planet 2, 5 or 6 = planet 3
2 planets - 1 to 3 = planet 1, 4 to 6 = planet 2
No need for 1 planet as both would be assigned automatically.
Okay, not great rules, but they do help if you want to get some practice.
All the best.
Richard