Well, took me a hell of a long time to complete this level, and a hell of a lot of attempts. You need to build up your defences very quickly before the first attack from all three houses. Upgrade to get Turrets ASAP. Harvest as much spice as possible in as safest place as possible.
Assemble all your units around your turrets and have Rocket Launchers to back them up. Use the Rocket Launchers to take down the annoying enemy rocket launchers who manage to stand just out of reach.
If you can last through that first attack, then rebuild your defences. Keep your army at the front of the base also and begin all the upgrades, etc. Keep a constant Freman attack on the enemy and take each enemy out one at a time.
Ordos are usually the easiest to take out, then the Harkonnen and then the emperor. Sonic tanks are usually the most effect but make sure you use a variety of tanks.