Rules
The Predator is a Tank with AV 13/11/10 on front/side/rear armour. This means it is a tough nut to crack with a frontal bombardment - auto-cannons require 6s to glance, and krak missiles will need 6s to penetrate. Its the AV 11 side armour that is your biggest weakness, allowing light anti-tank guns to rip you apart if they can deploy or maneuver into the right firing position. You must protect those flanks and force your opponent to face either AV 13 or a 3+ cover save on the side armour.
Rear armour 10, shared by most other vehicles in the game, means that you are vulnerable to assault. Unfortunately for the Predator, it is most effectively utilised when stationary - and this means that units in assault are hitting you automatically! Deciding when to move and reduce your rate of fire is the key to effective Generalship with this tank. Or you can take the easy way out - Blood Angels pay a handful more points to make their Predators Fast, which is an absolute bargain and totally unfair for us vanilla players ;-) But that is for another article...
Make sure that you understand the rules for sponson line of sight before you field them on the battlefield. As far as I can make out from the rule book diagrams, line of sight is calculated from the base of the weapon where it attaches to the sponson, not the tip. Its important to understand the angles that you need in order to bring all your weapons to bear on a target.
Don't forget the option to Tank Shock if your Predator is shaken, or in the rare circumstance that it has had all it's weapons destroyed without being immobilised. AV 13 and a 9"+ move gives you a Strength 7 attack that could do something useful!
Predators come standard with smoke launchers and a searchlight. Smoke launchers are useful when the Predator can't shoot - either because it is out of position (your bad!) or has been shaken by enemy fire. In these cases don't forget to pop smoke and love that cover save! Searchlights aren't much use, as a Predator can't start on the table in a Dawn of War scenario.
Predators come standard with smoke launchers and a searchlight. Smoke launchers are useful when the Predator can't shoot - either because it is out of position (your bad!) or has been shaken by enemy fire. In these cases don't forget to pop smoke and love that cover save! Searchlights aren't much use, as a Predator can't start on the table in a Dawn of War scenario.
Weapon Options
The Predator comes with a single turret auto-cannon by default; an effective light tank destroyer and monstrous creature wounder. It's hard to pass up adding the optional heavy bolter sponsons - for a good price you gain a strong anti-infantry ability with 8 high Strength shots at AP4. This is enough firepower to force a moral check, or wipe out the dregs of a unit.
Of course the upgrade options do not stop there. All the above guns can be swapped with lascannons - or a twin-linked lascannon in the case of the turret autocannon. But these upgrades come at a price, and so should only be chosen if they cover a weakness in the rest of your list. Because of the vulnerability of the turret twin-linked lascannon to weapon-destroyed results, the usual choice is to upgrade the heavy bolter sponsons. Also the lascannons and auto-cannons are complementary weapons against most targets.
Of course the upgrade options do not stop there. All the above guns can be swapped with lascannons - or a twin-linked lascannon in the case of the turret autocannon. But these upgrades come at a price, and so should only be chosen if they cover a weakness in the rest of your list. Because of the vulnerability of the turret twin-linked lascannon to weapon-destroyed results, the usual choice is to upgrade the heavy bolter sponsons. Also the lascannons and auto-cannons are complementary weapons against most targets.
Other Options
Yes there are other options that can be added to the Predator - but the prices are generally not worth the extra value provided. To be honest I have never taken any of these.
You can add a pintle-mounted storm bolter, giving additional anti-infantry fire that complements heavy bolter sponsons. But it does not complement the auto-cannon, so in scenarios when you are moving and firing at tanks those points are wasted. And in any case spending so many points on a couple of Strength 4 shots is generally not worth it.
Extra armour is even less useful - its actually pretty rare for a vehicle to be stunned, and for a shooty tank like the Predator retaining the ability to move is far less important than for a transport. Give it a miss and save valuable points. You might find the occasional use for a dozer blade but once again this is a far more useful upgrade for a transport vehicle, that actually needs to get somewhere to drop off its passengers. Just avoid difficult terrain!
Finally is the hunter-killer missile option. This is a weapon that complements both auto-cannons and lascannons, and can either be used to maximise an opening salvo or saved for an efficient shot at side-armour. Not really an optimal selection, but I can see the potential in the right list. Probably something I should investigate further on the battlefield.
Example Units
Dakka (85)
Predator with auto-cannon, 2 heavy bolter sponsons
The most commonly fielded Predator configuration. Cheap and effective against a variety of targets - and three of these are cheaper than a single Land Raider! Suffers from an inability to threaten AV 13-14, but is cheap enough that this rarely becomes an issue.
Hybrid (120)
Predator with auto-cannon, 2 lascannon sponsons
The perfect compromise between the price of the Dakka and the anti-tank power of the Annihilator - but sacrifices the anti-infantry ability of the Dakka configuration. Able to move and fire a lascannon, or sit still and blast vehicles off the table, its a good choice when you need to up your armies anti-tank firepower.
Annihilator (165)
Predator with twin-linked lascannon, 2 lascannon sponsons
This is the most vicious long-ranged anti-tank configuration in the Space Marine arsenal. If it gets a chance to fire it should be able to comfortably cripple an opposing vehicle each turn. However it has giant SHOOT ME signs painted on the armour, especially that AV 11 side armour. And all it takes is one shaken result in order to stop all that shooting for a turn. Field it at your own risk!
This is the most vicious long-ranged anti-tank configuration in the Space Marine arsenal. If it gets a chance to fire it should be able to comfortably cripple an opposing vehicle each turn. However it has giant SHOOT ME signs painted on the armour, especially that AV 11 side armour. And all it takes is one shaken result in order to stop all that shooting for a turn. Field it at your own risk!