-Avoid attacking the enemy, let them come to you. When you start, do not build Weapon Factories. Instead, build Cannons and Missile Turrets. It is a good idea to build Trikes and Quads to act as scout lookouts. Don't build too fast or you will run out of money when they attack. The most important thing is to not put all of your defenses in one place.
-Use the following strategy as the Atreides for an easy win. Defend your base openings in later, tougher levels, by blocking off all entrances except the main, largest entrance. With the others, build a double wall to provide cover. After that, with the central entrance, build across it, block by block, not with gun turrets, but rocket turrets. In order to hit the enemy Missile Tanks, you need to match their distance, and for the units that cannot hit far, pummel them with several rockets at once, killing them before they get there. Build them across all but one block (a gate), so your units can get out. Then, continue to build up an army consisting of Rocket Soldiers, Grenadiers, and Riflemen; Trikes and Quads; and Combat, Missile, Seige, and Sonic Tanks. At least 100 Units in all. 30 Soldiers will do fine, mainly rocket and grenadiers to destroy turrets and buildings for your vehicles. Also, build a Secret Squad consisting of 25 Fremen (have machine guns and rockets to deal with soldiers and vehicles/buildings; will be the enforcers, dealing with stray opposition. These forces will come during the main attack, while enemy forces are distracted by Sonic Tanks, Group Square, etc. Try finding a no-turret zone to enter the enemy base) and 20 Engineers (what the Fremen are defending; can convert enemy buildings. While the main enemy forces are being slaughtered by your own huge forces, sneak in, kill any stray enemies, and convert their Construction Yard first, then Barracks, Heavy Factories, Light Factories, and finally Wind Traps to kill all power). Now build up Special Reinforcements, and perhaps a mop-up crew consisting of 50 different soldiers.