The others start in the rank of commander, so you have to extend the rank of lieutenant-captain as long as possible. Lieutenant approx. you can win a day by taking your fleet to the bottom of the map before Thorin arrives, so Thorin must travel through the entire area (because it always appears next to your fleet) before the Garthogs arrive.
As captain, it’s worth waiting for both viruses to be destroyed on the planet New Caroline, and only after telling the colonel that there are suspicious virus infections. Then you don’t have much influence on the thing anymore, at most that you attack the prototypical Garthog fleet after leaving the planet Achilles. Here’s to be careful, because when they get close to the planet Garthog 4, the message immediately comes from the colonel that you’re down, which tends to just shorten the game.