At the start of the game, build 2-3 Mass Extractors and Power Generators, then a Land or Air Factory. The Land Factory should build a few T1 engineers as well as the usual assortment of ground units. To keep your early economy optimized, have the Commander finish building the Mass Extractors in your immediate area, then start constructing more factories with a few Power Generators next to each so that you don’t run out of energy. At least one Engineer should be patrolling any trees or rocks near your base for an early economic boost, while another builds more Mass Extractors and a third builds a Hydrocarbon Power Plant if you have one near you, or Power Generators if you don’t. At this early point, it’s often preferable to build land scouts instead of a T1 radar tower.
You’ll usually want both Land and Air Factories early on, with the Air Factory pumping out fighters and the occasional bomber. Naval Factories are a bigger investment, but establishing an early sea presence can force opponents to waste valuable resources on defenses or subs. It’s also possible to kick an opponent out of the air by patrolling your fighters just outside his base so that any fighters he builds are shot down. Don’t tech up until you have multiple factories, as you don’t want to be cut off from producing units. Don’t forget to upgrade your Mass Extractors; it’s cheaper and safer than building Fabricator farms.