As far as specific mechanics go:
If you don't have any units, you first need to build a factory to make a unit so you can capture the nearest recruitment site so you can build a recruitment centre so you can get enough recruits to build units so you can start to expand, while also building up defences for your base. During this process you may find yourself with the mouse cursor hovering over a build button waiting for the recruit count to go up enough for you to do something.
Along the same lines, I think an understated and underutilized mechanic is just simply capturing as many sites as possible with your starting units. Not just recruitment sites.
If you have a 3-1 unit advantage that can snowball very quickly by getting capture bonuses. The territory is useful but the precious early recruits are even more valuable in terms of pressing your advantage.
