The classic tactic is to put your constructor to work on a Light Vehicle plant while the Engineer works on storage units for the mining station and connectors between the plant and the mine. Extra engineers can set up some fixed defenses, like anti-air, radar, and missile installations. Early on, you also need a heavy unit plant to build the major fighting vehicles, and an air unit factory. Once you have these facilities working, you're left to decide which units to build in them. Early on, scouts are always useful.
Extra surveyors can be good if there is a lot of land to check for vital resources.
Engineers and supply trucks will always find work, too. Which air units to build is always a good question. And ground attack planes can be devastating. Since airplanes never have to land except to rearm and be repaired, they're best used at the fringes of a conflict, taking out enemy constructors and engineers, moving columns without fighter support, and wayward surveyors and scouts. They don't have a lot of use in straight conflict, unless the enemy has somehow been deprived of anti-air units through an active ground offense or gunboat bombardment.