Sorium harvesting is probably the easiest. Create a ship with 250k - 500k fuel capacity, tack on a couple engines and a lot of sorium harvesters. Park in orbit around a gas giant with sorium.
Terraformers are maybe the second easiest. Create a ship with a couple terraformers, and move to the planet you wish to terraform. Then from the F2 screen (You'll need a colony on the planet), go to the terraforming tab and start the work.
Mining units... I've not used them much at all. I believe you need a colony, because the mined minerals get dropped onto the planet. If not, you'll need plenty of cargo space. Either way, park the ship with the miners in orbit around the target, and let it go to work. Move on to the next in the list.