Always train the maximum amount of soldiers possible
Always try to train elite military units in increments of 24(this is calculated automatically by clicking the blue numerical link next to the units)
You can also do some tricky stuff like training in intervals of 1,2,3,4,5 or whatever, to make your troops stay in training longer then normal, thus keeping your rax space empty for longer. So instead of seeing
2,2,2,2,2,2,2,2 all the way to 24ticks u will see
0,0,0,0,0,0,0,20 and those elites wont start taking up rax space until they finish
Until you have a high population, always train as many soldiers as possible. You draft those into more advanced military, so you can always save them for later, for when you can afford doing so.
Troopers and Dragoons and Tactical Fighters are offensive units only, Laser Troopers and Laser Dragoons are defensive units, Scientists research for your kingdom, and Tanks + High Guard Lancers can be used for both offense and defense. Some of the units need to be researched first, in order to be trained.
If you don't want to get attacked early on, you should train many Laser Troopers or Laser Dragoons. Ask sector mates or friends of about your own kingdom size how much defense they have, if you are uncertain about if your defense is enough.
Military Unit Type
Basic military units
Offensive unit only
Defensive unit only
Strong defensive unit
Strong offensive unit
Offence and Defence
Can research for you
No solider needed
Update: Troops 'in training' are now included in the Barracks Capacity.