You'll need to sit down with a pen and paper and think how your going to do it, you need to consider things like
the table structure of the database
How battles take place
units in game ie soldiers, vehciles, etc
Is the game going to be real-time or tick (turn) based?
Will you have tribes/clans/alliances in it?
What research and developments there will be
You probably from that get an idea of how much planning there is involved. One idea for the planning would be to write the help pages for the game and kinda use them as a template for coding some of the stuff.