When you get to the stage where you have no cash left and there is no spice to be collected, send your harvester to the enemy camp. It will be destroyed, another one will replace it and you'll receive a few credits. You can repeat this as many times as you like.
On slower systems to speed up spice harvesting click on a harvester which is harvesting spice and keep clicking on him. The percentage of spice harvested goes up with each click on the harvestor. (Note: On fast systems 030+ the harvester works at its maximum speed so this has no effect).
When playing as Ordos. Use a Deviator to persuade your opponents to change to your side. Once changed move this unit to a safe position and click on the attack button and wait. When the unit changes back to his natural colour click on the enemy vehicle or building you want this to attack. The unit will carry out your attack order but the enemy (his friends) won't attack him.
If playing as Atreides: Use a sonic wave tank to destroy or weaken (so that you can capture it) a Rocket Turret. This unit can attack from outside the Rocket Turret's range.
Otherwise use rocket launchers. If you are at the right angle, you will manage to hit the Rocket Turret but it won't attack you! You have to experiment a bit with this, as it isn't a 100% certainty. So be prepared to withdraw and try again from a different angle
In both instances be wary of the enemy sending out a tank to attack your unit.
Sonic Wave Tanks can be very useful for defense, but NOT close to your own camp as their blast may also damage your buildings. Try to find a bit of rock which is on the enemies path to your base. Position one or more Sonic Wave Tanks and leave them in guard mode. Enemy vehicles will drive past your Sonic Wave Tanks, even when they start attacking, That way your enemies are weakened and your base defences can finish them more easily.
If you have a Carry-all, make sure your Repair Facility is surrounded by other buildings or vehicles. That way repaired vehicles can't leave the Reapir Facility and the Carry-all will put it back where it came from. Otherwise repaired vehicles will drive just outside the Reapir Facility.
Always defend your base well with the best possible units. Until defensive turrets become available leave units on guard, never send them all out at the same time. Later on in the game, a group of well placed rocket turrets will leave you free to concentrate on attacking. Always place rocket turrets on the edge of the base so they don't interfere with future buildings.
To stop the Harkonen forces wandering into your base and smashing everything up, determine the direction of attack - as a rule, enemy units attack from one direction. Then build a line of around half a dozen concrete blocks extending from your base towards the enemy. Now build another line of blocks cutting across your first line at right angles, so that it faces the enemy. Now all you need to do is build rocket launchers along the wall and that should stop most units from getting near your base!
Don't forget to attack! The enemy will often send a constant stream of units at you but it is important to build up a force and take a shot at the enemy base instead of just defending your own. You can often find the enemy base by following his units back there.
On the later levels build a Starport. This is a very important building to own since it enables you to buy units from The Merchant's Guild for anything up to half the price it costs to build them! Keep checking for bargains, because the prices change everytime you look.
If you have a Heavy Factory or a Starport, either build or order a few extra Harvesters. This way you only need to build one Spice Refinery. You should have about three Harvesters to maximise spice production. Don't forget to build Spice Silos as the spice can build up quickly. If you are short on credits, sometimes you don't even need to build factories because the Starport will provide everything, usually at a cheaper price. The down side however, is that the Starport can run out of stock, which can be inconvenient.
A Repair Facility is almost essential once they become available. Carry-alls can bring damaged units to them and take them back to the battlefield.
If you capture enemy factories you can build their special units such as The Deviator, The Devastator and The Sonic Tank.
Watch out for sneak attacks especially near the start of a level. Your first encounter with an enemy house will often be when they airlift troops near your base in a Carry-all. The troops can appear on any side of the base so make sure all sides are guarded. After that you can concentrate your defences on the side of your base which faces the enemy one.
Your most important building is the Construction Yard (see attack plan). On the later levels the enemy will sometimes try to concentrate their attack on it and Death Hand Missiles are frequently aimed at it. If it is destroyed you can no longer build any new buildings, so guard it well. If you are unlucky and lose it, order or build a Mobile Construction Facility and deploy it where the Construction Yard used to be.
The Spice Refinery is another important building. If it is destroyed when you are low on credits then you won't be able to rebuild it because of the lack of money and you will not be able to refine spice to earn credits. In this dire situation, your base will eventually be destroyed, unless you have almost finished the level.
On the last two levels you will be allowed to build a House Palace. This can only be built once you have a Starport. It is very expensive (999 credits) but is extremely well armoured and is free to repair. It also gives you access to your House's Special Ability (Fremen, Saboteur or Death Hand).
When attacking, the most important building to destroy is the emeny Construction Facility - once you have done this they can't replace any of the buildings you take out. You should also concentrate on taking out the enemy defence turrets before finishing off the rest of the base.
Victory is almost assured if you destroy the Construction Facility, although the enemy usually has more than one of them in later levels. Until tanks become available, the Harvester is one of your most important weapons because it's a tracked unit and can be used to squash any enemy troopers or infantry sent to attack your base.
It's useful to have a Harvester guarding your base especially if you're fighting the Harkonnens, because they like using Heavy Troopers which can be very difficult to destroy.
Destroying enemy House Palaces is very hard because they're also free for them to repair. You have to launch an all-out attack mainly with Missile Launchers and Heavy Tanks to stand a chance.
Destroying a Palace can take some time, but you can afford to put all your units onto the task and provide air support with Ornithopters. In effect you have to damage the Palace faster than your enemy can repair it, but this can be done.
On the last two levels both opposing houses team up to destroy you. This isn't as bad as it sounds - it just means you need to defend your base a bit more against the extra units the combined enemy send in. It also means you have to destroy two bases instead of one.
You can also build Palaces on these levels - as can your enemies - and IX Research Centres which enable you to construct special units. If you use these units well, and follow the attack plan, these levels are not much harder than the others.
On this level you face the two enemy houses and the Emperor's Elite forces. This level is extremely hard compared to the rest of the game and you just have to muddle through. The enemies are always attacking in great numbers and you really have to watch out for Death Hands as the Harkonnens and The Emperor both have them - don't forget to save your position regularly. Keep the same attack plan since it's vital to start attacking even though your base is under siege from the beginning. Use an Ornithopter to determine the position of enemy bases since they're widely spread out over the opposite side of the map to you, usually to the North.
Remember enemies have at least two Construction Facilities on this level so it's important to hit them all. Isolate one enemy at a time and destroy them before moving on to the next and try to capture their factories so you can build the special weapons. Captured factories are often situated in strategic positions close to other enemies, which makes them ideal if your base is far away.
It's best to leave the Emperor's Sardaukar Base until last. The Sardaukar have large numbers of all the standard units which have been improved to elite status, coloured purple. The Sardaukar's Troopers are hard to kill unless they're run over by a tracked unit. They also have their Construction Yard very heavily guarded with a further Construction Yard hidden away in a corner, so it's important to explore the map.
The Sardaukar Base is also very heavily guarded. It has a double-strength defensive wall around it with lots of Rocket Turrets on the perimeter. The best way to destroy the base is by taking its Construction Facility with a group of four or five Rocket Launchers sited in a destroyed enemy base, so the Sardaukar cannot see them. A quick surprise attack on the Construction Yard with Rocket Tanks can destroy it before the Sardaukar can start repairs.
Now try destroying some of the defensive turrets and other buildings. Rocket Tanks are extremely useful, so keep them well protected unless you want them knocked out by a rogue Siege Tank.
If your enemy starts rebuilding, then they have a secret Construction Yard which must be knocked out. Do this and eventually the enemy's defences collapse, leaving the Sardaukar Palace to be destroyed. This is very hard to achieve, so you just have to pile all your forces onto it and wait. When the Palace is finally destroyed you've completed the game and can watch the end sequence.