Strategy is the bulk of the game, that portion of it played out on the map. Strategic plans are heavily informed by desired Tactics, especially in the realm of magic. Strategic goals always include procuring provinces, gold, gems, forts, and thrones of ascension in as large numbers as reasonably possible. Depending on details, there may also be specific provinces such as chokepoints that you desire, and there will almost always be specific spells you want to research and specific magic items you want to forge.
You should decide an overall grand strategic plan before beginning the game, and tailor your pretender to fit it. This plan should decide whether you want to win in the early game, mid game, or late game (according to the size of the map and your choice of nation). You should have a way to do that and ways to survive and grow in each preceding age, and it's best to have these in mind when designing your pretender.
The early game proceeds from combat against independent troops into, in some cases, an early war.
Expansion Is the art of seizing provinces from indies, expanding your borders without serious wars. The most important thing to do in the early game is to gain provinces before your neighbors do. This, fortunately, can be tested against AI and is therefore easy to plan for. If you can consistently get fifteen provinces by the end of year one, you have a good expansion plan. If not, consider whether the things you're getting instead are really worth it.
In general, you do not want to go to war until you've finished your expansion. Warring before this point will hinder your growth and may condemn both you and your opponent to irrelevance in games of most sizes. If you do find yourself in such a situation, fight bitterly to be sure, but if possible focus more on expanding while doing so than on defeating your enemy. Defeating an enemy entirely is very difficult early on, and the benefits of going quickly will rarely be worth it in the long run.
In small games, it can be advantageous to start and win a war as soon as you've finished your expansion. Powerful sacred units, even if cap-only, can help you win a war before your enemy is ready. Giants with N9 are especially good at this, but cavalry with W9 are also entirely proficient.
The middle of the game begins when you've got around Research 5 in a school or two. This is the era of big armies and head-to-head wars, and many nations have specific research goals which give them winning strategies that are only effectively beaten with superior research and specifically tailored counters.
This is the age of large groups of elites with big buffs. Blood does very well in the late game, because it scales well.
Tactics are the elements of planning that impact individual battles. Tactics are decided for an army prior to battle, but should generally take potential enemies into consideration as well. Tactical considerations are often the primary determiners for strategic decisions regarding the acquisition of forces and magical research.
The most fundamental concept of unit tactics is that infantry goes in front, to meet enemy infantry, fast units like cavalry go around the sides to charge the back and encircle or destroy enemy ranged units, and ranged units go in the back to be defended by infantry while firing upon the enemy. Because Dominions is made of fantasy nations with widely varying unit rosters, however, actual tactics my vary immensely, especially when taking complex magic into consideration.
All formations carry a small morale penalty, and as such are of subjective utility. An unformed (box) mass of troops is the best for many situations, though this penalty is irrelevant for undead or mindless troops.
Line formations are effective at making smaller numbers of troops defend larger numbers of ranged units. If defending a back line is the sole or only purpose of troops, line formation may be appropriate.
Orders are the actions that you tell a unit or commander to perform. They are your sole method of control over what actions units take during battles.
Straightforward attacking is often the best option. Attacking the closest unit will allow your armies to most easily charge them. Attacking the rear unit will allow you to deal large damage to vulnerable troops including expensive and important mages. However, attacking the rear is likely to be blocked against, and only largely successful when using flying units.
Generally like Attack for archers. Some ranged weapons (such as javelins) have very limited ammunition, in which case the unit will attack after firing.
You can tell your troops to wait for two turns and before attacking. This is advisable if your ranged capacity is going to do more damage to your enemies troops than theirs will to yours.
Aside from guarding commanders, this command is useful for archer traps. If you put a small group of units at the front of the army, archers set to "fire closest" will fire on this squad. If the squad is set to "guard commander" the units will then move towards the commander, who may be at the back of the battlefield, and the archers, in order to stay in range, will advance. This can force enemy archers to get in front of their would-be protectors, allowing you to wipe them out more easily.
Mages are scripted on a per-spell battle, with players selecting up to five spells and the Spell command generally used thereafter. Mages set to Spells will prefer defensive spells and simple spells such as evocations, so more complex magical tactics must be completed in five spells per mage or less.
The simplest thing that mages can do is use lots of evocation, or other such spells that directly impact the enemy. This can have a big impact if you use a lot of mages, but the choice of spell has a big effect, and there are counters. It also relies on relatively a large mage corps.
Troops are better when they're better, and a few powerful mages can supply powerful force multipliers to a large number of troops. Doing this well takes a high research level.