As the dark lord Sauron, your primary task is to capture the Cities and Strongholds of the Free Peoples for a total worth of ten victory points. These can be found in different locations in Middle Earth and it is important that you plan which victory point locations you are going after during the first turns of the game so you can build your strategy around it.
The most obvious victory points area is Gondor: Pelargir is only two Regions away from the Southrons and Easterlings in Umbar and Near Harad, and Minas Tirith is only three Regions away from Minas Morgul. Taking all five victory points in Gondor also has the added bonus of making it impossible for Strider to be crowned as the rightful heir to Isildur. These might seem like easy pickings if you strike fast and hard and Pelargir is most times an easy victory point since it is only a City, but Minas Tirith can be a tough nut to crack without elite units to keep the siege going. Here the Southron and Easterlings' elites can be used to support the siege but by doing so you forgo the possibility of moving the Southron and Easterlings along the coast to besiege Dol Amroth. The problem is that for Gondor to fall quickly both the Sauron nation and the Southron and Easterling nation must be brought to war and for you to reach Minas Tirith you must first take Osgiliath. This will activate Gondor and the prudent Free Peoples player will have moved Gondor one step closer to war on the political track if he sees this attack coming, enabling him to muster defenders in Minas Tirith.
The second most obvious victory points area is Rohan. Helm's Deep is only two Regions away from Orthanc and then Edoras is only two more areas away. A quick mustering of Isengard and Saruman will most often net you Helm's Deep in the third turn of the game. If the assault on the great fortress of Helm's Deep goes according to plan you can quickly continue on towards Edoras and another victory point. The problem here is if Gandalf the White has emerged in Fangorn or any Rohan Region since with him comes the danger of the Ents launching their attacks on Orthanc. The Ents can be a powerful deterrent that can force you to keep quite a big army holed up in Isengard to protect Saruman from the potential Ent attack and the other part of your army in Helm's Deep just to keep it safe.
The reason I have called Gondor and Rohan the first and second most obvious targets for your armies is that players tend to follow the book the first times they play the game. This is natural but after a few tries the other possible victory points locations become tempting to try and some of them should be even more tempting than both Gondor and Rohan.
The most obvious of all the victory locations should be the DEW-line; this is the area in the northeast portion of the map where Dale, Erebor and the Woodland Realm are situated closely together. Here a combined attack from Dol Guldur and Rhûn should be able to capture five victory points. By sending the Easterlings from North and South Rhûn into Dale and the Dol Guldur garrison to the Old Forest Road you should be nicely situated to launch an assault on the Woodland Realm. If reinforcements are needed they can quickly be mustered in Dol Guldur and North Rhûn. Once the Woodland Realm has fallen, Erebor should be easy pickings unless the Free Peoples player has managed to get the Dwarven nation to war. If this is the case the strategy is less foolproof. If the Elves or Dwarves are allowed to muster before their Strongholds are besieged they might prove too strong.
To the northwest lies three victory points in the forms of the Shire and the Grey Havens. An assault launched from North Dunland, preferably by the "Rage of the Dunlendings" card, can easily recreate the scouring of the Shire and bring in another victory point. The same can be achieved by some mustering in Angmar, possibly with the "Return of the Witch-King" card.
If you aim for the Grey Havens as well make sure you bring a large enough army with some elites to take both Settlements without needing reinforcements since it is a long way to the Grey Havens.
Now we are left with the two Elven sanctuaries of Lorien and Rivendell. Both can be reached from Moria, but Lorien is closer and an attack on the Golden Wood can be supported from Dol Guldur. If you aim for Lorien do it quickly since this will rob the Fellowship of a much-needed haven to rest and heal in. Rivendell is a bit tougher to take by simply marching an army there from Moria or Angmar and Mount Gundabad. There is however an event card that is ideal for this. By playing "Monsters Roused" you get a force that with only very little support can take out the Elven Stronghold.
Having looked at the different victory points location I will try to point you in the right direction of how to plan your campaign. First take a look at what cards you are dealt at the beginning of the game. If you are lucky to draw some of the really nasty cards like "Wormtongue", "Denethor's Folly", "Balrog of Moria", or "Monsters Roused", you might as well let that guide your decision as to where to strike first.
Secondly take a look at what the Free Peoples player does; does he take Gandalf as a casualty early? Perhaps he has an Ent card? What card is he playing? What nations is he trying to activate? If the Free Peoples player plays a card like "Book of Mazarbul" you might want to stay away from the DEW-line since the Dwarves from Erebor can quickly strengthen Dale. If he sends Strider to Edoras there might be a risk he is holding the "Dead Men of Dunharrow" card and your armies in Gondor could be in peril.
Thirdly try to keep him guessing as to where you will strike, fake a build up at one of his Strongholds and then once he has recruited some troops there avoid it and strike where he is weaker. Remember that you have an unlimited number of troops, your opponent hasn't.
Most importantly, try to strike at the right time, launching a big army against Minas Tirith right after Aragorn has been crowned there and the Gondor army there is composed of three elites and five regulars might prove an unwise decision while using the same army to bypass Minas Tirith and strike at Edoras, which is only three Regions away, instead could be just what is needed.
Remember to vary your strategies so your opponent doesn't know where you will attack. If you went for Gondor and Rohan last game try some new strategy this time around.