Unlike most strategy games, the campaign doesn't seem to be designed to walk players through the game mechanics while holding their hands. The Dread Lords require a player to know how to deal with them, and a starting player simply won't. You'll have a much better experience if you play a few sandbox games to really learn the game, then tackle the campaign. Sandbox mode is what gives the game its replayability, many players never even bother with the campaign.
That being said, you need to rush several tech areas to even have a chance. Weapons, miniaturization, and logistics are most important. Once you are pretty well advanced, build fleets that have enough offensive power to at least triple the Dread Lord's defense + HP. If you have them spread over enough hulls, one fleet may have a chance at taking out a ship; bring at least two fleets, just in case.
If the Dread Lords get a ship out and start attacking, build a lure - a ship for them to chase, but fast enough to keep ahead of them once they start chasing it. One cargo hull with engines and life support can take a ship efffectively out of action without ever taking a shot at it.
Above all, the trick to beating Dread Lords is speed. The earlier you hit them, the easier it will be.