I actually wanted to post a full guide, but that would take a bit too much time. Here’s some general tips that I myself use when playing. They unfortunately mostly apply to 1v1 situations:
1. Pick your territories wisely (disregard this number if it’s automatic). Starting out in a gigantic bonus will take you too long to receive an edge. Starting out in a bonus of 1 with 1 territory will give you that edge right away. Take note of the surrounding bonuses. You’ll want to be able to expand quickly and get a high income as soon as possible. If you can take multiple territories from the start, try to fully capture a bonus. Also make sure to pick more territories than you will receive, to make up for the fact your opponent may choose the same. These territories should be in an area further away to make sure you can build up if your opponent has the edge in your initial starting position.
2. Take note of the analyse button. This will show how much of a chance you have to capture the territory you attacking with the number of armies you’re attacking with. A 25% chance is really far too low. A 100% chance is nice, but that usually takes too many armies. I’d go for something like 95%. Versus neutrals with 2 armies, it’s usually best to attack with 4 or 5 armies.
3. Always aim for taking a bonus first. It’s nice that you can attack a territory further on, but if that means you’re less certain of taking your bonus, you’ll be worse off. If you can’t take a bonus within this turn, make sure to attack territories that will reveal the required ones so that you can take it next turn. If you can take a bonus within this turn, but you’ll have to accept lower chances for each territory, take that chance! Better to attack the last 4 territories of a bonus with 3 troops and have a chance to take the bonus than to attack 2 of them with 6 and be certain that you won’t get the bonus this turn. It is not necessary to attack all territories within a bonus if you’re not able to take the bonus any way (such as due to unreachable territories at the moment). Rather, attack a single territory that will reveal them all and focus your current troops elsewhere.
4. Defensive behaviour generally works better than attacking in situations where you know your opponent might attack. If he is bound to attack your 1 territory with his 1 territory, put troops on there more than what you believe his income is. His attack will fail, and he will lose more troops than you in the process.
5. Order timing is key to victory. I found there’s generally X types of moves you can do each turn.
I: Attacking your opponent.
II: Transferring forces to a territory that may be under attack this turn.
III: Attacking or transferring forces to a territory that is not under any danger.
IV: Attacking a neutral territory which you’re aware of your opponent might attack next turn.
It is important to place these orders in the right way. Attacking your opponent is generally the last thing you’ll want to do (the one who attacks first will lose the most amount of troops), while attacking a neutral territory with increased forces your opponent might also attack is one of the first things you’ll want to do (you’ll have more troops on the territory than a neutral, so not only will he lose more troops than he initially thought, he also might not be able to take the territory). This is the order I generally place them in: II, IV, III, I. So I first transfer to a territory which may be under attack, then attack neutrals your opponent may attack, then transfer/attack territories without danger of your opponent, then attack my opponent directly. This is optimising your defensive advantage to the maximum.
6. The more moves you make in a turn, the more likely it is that your opponent’s attacks will happen first (thus giving you defender advantage). If you have a lot of troops to transfer to the frontline when they are not nearly there, it is very helpful to move them in separate groups (the more, the better). This is mimicking the effect of the order delay card, which creates a lot of “dummy moves” to allow some of your movements/attacks to happen after your opponent’s (more on cards later).
7. When you meet with your opponent, it is generally best to assess whether you think you have more income and whether you have the element of surprise (you may have a lot more troops on the territories of conflict). If yes, it is generally a good idea to create a massive army and attack him head on (as the last move, of course). Matches are won/lost easily once a large army breaks through an enemy’s defences.
8. Deny bonuses to your opponent. If you’re able to break through his defences, he will have more and more trouble keeping you out. Attack his most dangerous bonuses to prevent him from building back up. You only need to attack a single territory of his bonus to remove the entire income.
9. When you face multiple territories with 1 army on it bordering with one of your own, and you can place a massive amount of troops, attack some of the territories with 2 or 3 armies and attack one of them with your main force. Your opponent is forced to defend either one of them with a big force, or all of them with small forces. If you merely attack one point, you have the chance to face that big force of his. If you attack multiple, you’ll deny him his bonuses even though your big attack may fail (the other way around if he defends them all equally).
10. If you are in the position of having multiple territories facing one of his, assess whether you believe you have more income than he does. If yes, as mentioned above, attack his territory as the first order so that you’ll take away his territory before he can attack. If no, place some small troops on each to prevent the strategy I mentioned above and regroup further on: your territory is lost any way. You’ll want to have an easily defended location.
11. Cards are important. Order priority and order delay helps getting in those orders at the correct moment with even less luck involved. Reinforcements are handy for both expanding and defending/attacking. All of them have their uses (even though some much less than others).
12. Small tips for games with multiple opponents, try to make temporary alliances. If you meet an opponent in the first few turns, ask him to not attack each other for a while. Attacking each other will only make you weaker against the other opponents, and the both of you will lose. In team games, try and gang up on single opponents. 2v1 is generally an easy win. Defeating one of them almost ensures your victory (unless in very big team games, such as 12v12).