Tips for Newbies
Start buying marines as soon as possible. Also, look for a good Marine Officer with 5 stars as early as possible. These will make your life much easier. Easy targets will be PMC freighters once you get to the point in the story that they turn hostile.
Stack multiple “build X station in Y sector” missions (ie: “build energy array in inner world”). Build 1 station and all the missions complete, meaning you get a nice subsidy for your station.
Building additional stages counts as building a station for the purposes of missions.