I have noticed that in the earlier missions they seem to use Doom Rays, and huge amounts of them. Not that I managed to beat them, so I ended up taking my "Ultimate Strategy" and ran away...
In the early game though their Logistics is poor and they cannot make fleets. Presumably, with constant bombardment of large fleets consisting of small or medium hulled ships.
Use the best weapons tech you have (Mass Drivers is reasonably good early game in the campaign due to it's good balance between price/power/space). Don't even bother with defence, it'll take up space and will have little effect against their advanced weaponary, use the space for more weaponary.
If you need to invade their planets, put transports in fleets of 3 or 4, as the dread lords soldering ability is immensely high and, with the 10/20 soldiers they ahve on planets, they can take out your soldiers by the thousands.
It's likely that their planet is far away from your starting system, so you can use starbases to increase your range, but don't leave them unprotected as the Dread Lords will almost certainly destroy them.