This is a technique that worked very well when I was writing my armies for Sword Warriors.
1)Draw a chart with D4-D20 on the bottom. The sides should be marked from 0-100 as in a % situation.
2)Determine the 'False' mean of your army scores. This means that you want to mark on the map the middle of the line for your army. Now lets say my army has a D10 mean. I put a circle on the D10 and lets say 60% spot. This means that of ALL units in the army (TYPES NOT ACTUAL NUMBERS!) the mean is a D10. A further note. If I have 100000 infantry and 5 tanks. Its not the average between the 1000006 soldiers. Instead its the average between the two; Infantry and Tanks.
3)Draw 'Liners.' This is a false statistical operation . But Liners are a sort of representation of where your army distributes its high and low. Aka are there alot of D6 units in the military? Or are there 50 D6 and one D20 messing with the average?
4)Think about the bulk of your army. Where is it located? Do you have 10000 infantry? Now make a 'goal post' in the area MOST used by your potential soldiers.
5)Determine how many types are OUTSIDE the bounds. A steep slope usally means one or two; and a smaller slope may mean 1-2. The major area in between the goal posts will give you about 50-60% of the overall units you determine.
6)Write stats for the units.
This KIND of works as a balancing platform also. And give syou a good visual representation of your army to work off of.