My tactics, as I've said, are differed and usually effective. I aim for a balanced defense and sustained offense to keep the enemy from ever building up enough to overrun me.
You can always improve on what you have. If nothing is happening in the game, start creating units to join your defense.
17th Century Defense...
Consists mainly of Pikeman, light or heavy cavalry and perhaps musketeers. Well trained Pikeman are extremely effective in forming spear walls and then holding there ground. They can repel any raids of mercenaries, medium sized cavalry attacks and other Pikeman but need the help of cavalry to take out musketeers. Why? Because if pikeman move from their position to fight a small group of musketeers, they become susceptible to another cavalry attacks which aren't so easy to repel when not holding ground. Have your cavalry mop up opposing musketeers, but be forwarned: A small group of cavalry is easily cut down, so don't be scared to send a formidable sized cavalry unit. I don't fully recommend using musketeers as your main line of defense for a while, but they do well in a supportive position.
A beautifully orchestrated defense against cavalry
The role of artillery...
is to make sure the enemies formations can't be given a chance to organize before an attack. If you have a lot of cannons firing at an enemy trying to organize formations or postions or artillery, they may lose their chance to organize and may send their units into a headlong frontal attack that cannot be fully carried out as they had planned. You need to make sure you have some good accuracy upgrades or the cannons will do crap. Cannons also come in handy when the enemy finally does get to your lines as they fire flattening grapeshots. 10 cannons can stop an entire attack on their own, as long as they're well guarded.
18th Century Defense...
Is not very hard to conduct. Since you don't have to switch around pikeman and musketeers to serve on your lines of defense (18th Century Musketeers are two in one) Things are far less complicated. Musketeers should form a tight wall around your civilization. If this is not possible (75% of the time it won't be) Have enough quick cavalry to support defensive muskteers and patch up any spots musketeers can't cover. It is good to have some reserves while on the defensive within your city, but don't put many there and don't make your reserves expensive troops. If your reserves are expensive, they might as well be on the front lines. If it comes down to your reserves anyway to save you, it hardly matters anyway. Chances are they won't.
There is no diffinitive strategy or tactic. Your strategy will have to differ for each situation you encounter.
17th Century Offense...
Is rather simplistic due to the sameness (is that a word?) of units. Your offense can be greatly helped by cannon superiority. In fact sometimes, it is not even an option to have no cannon superiority, you must have it. Times when you need cannon superiority are when the enemy has a large number of cannons or when you are attacking a heavily defending place, like a city.
But besides cannon superiority, you will also need a huge number of cavalry. In the 17th Century, It is extremely difficult (although not impossible) to break a defense without cavalry. But cavalry charges cannot work by themselves. They assault walls of pikeman about as well as throwing a cupcake at a wall. They splatter. So they must be supported and used correctly in the heat of battle.
18th Century Offense...
Is also rather simplistic. With multipurpose musketeers and extremely effective cavalry units to back them up, you can dominate the battlefield. Before launching a major 18th century offensive, first you should have mangolfier. It is only $1,795 gold to most nations and triples the effectiveness of units because you can fight the enemy before they can get to you and you can find the weakest spot in their civilization with it. 18th century offensives should not be sustained as much because they are far more expensive and slower to create. So, you'll need your heavy cavalry backed by many, many musketeers who are back by cannons. In front of the musketeers, multibarreled cannons are also quite effective and maybe even some light cavalry and pikeman to defend the musketeers and to be cannon fodder for them.
Introduction to Tactics
My Tactics
For Defense...
For Offense...
