The intention of this guide is cover standard MP settings and practices - not strategy or game mechanics.
I originally wrote this up for the Boot Camp game. I'm about to start another newbie game and rather than repeatedly posting this I figured I'd just link to it.
I have some more sections in mind that I'll try to get to soon.
Conceptual Balance Mod
CBM is used in most of the MP games that I am aware of. After you have played both CBM and vanilla, you may decide that you prefer vanilla. If so, no problem. The only "right" way to play the game is in a way that you find fun and, if it is MP, that you can get others to sign up for. These days you will have a smaller pool of players than a CBM game would but you shouldn't have a problem getting a game going (some players don't like CBM, others like both CBM and vanilla games). The main game type that I think would be difficult to fill is a large vanilla game (say, all nations in an era) because of the challenges of gem generators (clam of pearls, etc.) in such a situation.
So, if you're new to CBM what should you keep an eye out for? A lot of what CBM does is adjust prices in gems or gold in order to make under-utilized units more appealing. Perhaps the most popular, and easily noticeable, of CBM's changes has to do with pretenders. Most of the changes involve decreasing the cost of rarely used pretenders to make them more affordable (take a look at the various titan and human pretender chassis) . Occasionally pretenders are given abilities like summoning allies. However, in a few cases, underpriced pretenders have had their cost increased. So if you have been playing Pangaea or Sauromatia and choosing the gorgon pretender you'll notice quite an increase in cost under CBM.
Another area to keep an eye on is the gem cost of summons. Sadly, it is hard to justify spending the gems on many summons in a MP environment. Let me give an example. Let's say I'm playing Machaka. In the vanilla game I can summon a fire drake for 8 gems. That's a pretty steep price. In CBM I can summon them for 4 gems - much better! But then there's this Dragon Master spell. It let's me summon three drakes instead of one. That's great! Hmm, but it's Enchantment 8 and costs 30 gems. By the time I reach that how much of a factor will drakes be in the game? But wait a second, under CBM Dragon Master is only Ench. 3 (and only costs 5 gems to boot). My army of fire breathing drakes will be on the march in short order! Now this example is a bit different than most in that it involves two spells working together. But you will notice many price decreases on troop summons. Where you won't see them much is on thugs and SCs who, due to their power, don't need a drop in price.
As far as combat spells go look through the spell lists in-game. There can be differences in casting level, casting requirements, and effects compared to vanilla. Global spells can be very powerful and even game winning. They can also be kind of lame. So some them have had their level or costs increased and others the opposite (I still don't think the lame ones get cast much).
There are also a number of forging changes.
Cleveland's item forging reference is a great way to see at a glance what forging costs/requirements are for both vanilla and CBM games.
Endgame Diversity Mod
The EDM adds a variety of thug and SC summons in the four elemental paths and nature. The goal is to provide alternatives to Tartarians in the late game. In case you're not familiar with "Tarts" the way it works is this: Tartarians are the only non-unique, non-national SC available. The catch is, most of them are feebleminded and the only way to heal them is to have forged (or wished for) the Chalice or to have cast Gift of Health. This means that at most two nations will be able to take full advantage of tarts. Oh yeah, they also provide you with tremendous magical diversity and they're cheap. So you can see why games so often fall into a pattern of Constr. 8 (for the Chalice), then Conj. 9 (pick up Well of Misery along the way at Conj. 8).
The EDM helps address this by providing alternative, non-unique SC options. Tarts still have an edge in price and, especially, magic diversity but the situation is much better than without the EDM.
Diplomacy
When I admin games I normally I never say anything regarding diplomacy but since this is a newbie guide and the Dominions community may be different than other games you've played I thought I'd mention it. Probably the most common diplomatic message in Dominions is "NAP 3?". This asks for a non aggression pact with 3 turns notice before launching an attack if either party decides to end the NAP. So, that's worth the virtual paper it's written on, right? Well ... not exactly. The reality is that the terms of diplomatic agreements are usually honored. Some people don't like this, feeling it makes games too static, but even many of them will say they've never violated a NAP. Why? Partly because there's consequences in the game in which you're involved. Usually such situations devolve into charges and counter-charges but if the rest of the players come to believe you did in fact violate a NAP they will view their own agreements with you as being suspect. They may also be less inclined to hesitate at violating their own NAP's with you.
Then there's the impact it can have in other games. I want to make it clear that carrying a grudge from one game to another is
not acceptable. But there's another aspect to consider. Many Dominions players are very pragmatic and diplomacy is just another variable to consider. All other things being equal, if given a choice between dealing with a player they know sticks to agreements and one that they believe has violated an agreement, they will go with the former. It doesn't really matter if you were role-playing in the game in which you violated the NAP - you are still unreliable vs. the other player who is a known quantity.
Having said all that, even players who always honor NAPs will consider them void if you engage in certain actions. Burden of Time is a good example of a global that would be a cause for voiding a NAP immediately. Game winning globals such as Arcane Nexus and Forge of the Ancients would also qualify. Sneaking combat forces into the player's territory would also cause most players to consider a NAP void if they are discovered. Then too, some players who normally wouldn't violate a NAP say they will do so if they think it will win them the game - the stakes are then high enough to be worth it.
All that is by way of background as to the common practices in games I've been in. Unless a game admin specifies otherwise diplomacy doesn't have set rules.
One last thing. Diplomacy is an important part of Dominions. Even the most tactically skilled player will fall under the weight of enough attackers. If that same player can use diplomacy to turn one or more attackers into neutral parties, or even allies, the equation changes considerably. But don't expect great results if the only effort you put into it was to agree to a NAP 3 a few dozen turns ago. Of course don't pester people non-stop either - then they might attack you just out of annoyance.
BTW, because diplomacy takes time and can lead to dogpiling many players will mix in no-diplomacy games. In these games you cannot have any contact with others players (no NAPs, no trade, etc.). Taken to a further level, a RAND game (Random Anonymous No Diplomacy) will conceal the identity of players by randomly assigning nations.
Ok, one other thing. When you end a NAP (or someone ends it with you) I would recommend specifying what turn attack orders can be given and when the battles will take place. Both players can have the intention of abiding by the terms of the NAP and through a misunderstanding one attacks earlier than the other expected. It's worth the effort to be on the same page.
"Things are going too slow, I'm going to join more games"
Don't. Really, think twice before you join more than 2-3 games. Turns can literally take a minute early on but if you enter a half dozen games and they enter the mid-game at the same time you will almost certainly regret it. If you have that many late games going on you'll be cursing yourself and looking for subs (or staling and abandoning games, which is poor form). Start with just a couple of games and get an idea how much time the mid and late game take. Once some of your games have progressed you can manage it so that you have, for instance, one late and one early game. But for now you are better off just signing up for a couple of games and exercising patience until they develop.
BTW, you can use the extra time you have now to test some of your strategies so that when the mid game arrives you have a plan of attack in mind. You can also try a duel with another player. These aren't to everyone's taste but they play quickly and with only two players it is easy to agree on house rules (for instance, a 10 turn NAP to begin the game in order avoid an immediate rush).
Introduction to Dominions Multiplayer
Linear Mode
