Always use 'Fire At Will' when you are close-in to the bow or stern of an enemy ship . . . . the automatic targeting will be towards the centerline.
Firing a broadside in these circumstances will send half your shot to either side of your enemy.

Don't wallow. Changing direction too much, too often, and too fast, makes your ship roll (called "Heeling"). The most vulnerable part of the ship is the hull, and if you see copper sheathing, you are heeled over too far. Likewise, if you time your shots well, you'll fire into the bottom hull copper sheathing of the enemy.

Simple things oft make a difference . . . try to avoid being shot while your hull has rolled enough to show copper. By steering into your opponent, just as he fires, you will tend to roll your hull down.
Additionally, when you have full sails up, the lever action of wind and wave will heel your ship over, exposing your copper bottom.

Another simple tip: you turn through the points of the compass faster when you have reduced sail.

Wind . . . if you are upwind, you have the "weather gauge", and this is a great advantage, it is you who decides when and if to engage the enemy. And your shot will carry another 25 to 50 yards with the wind . . . fire on the uproll boys. In the days of sail, captains would maneuver for hours, sometimes days, trying to gain the weather gauge on the enemy.

Wind . . you CAN sail upwind (much more than you would be able to in reality). In multiplayer battles watch out for teamates (or yourself), sailing downwind away from the pack . . . . if you need help, unless they have a steam ship, they will take a long time indeed beating back upwind to your aid.

When given a directional order from your Admiral, such as "Steer SW, Full Sail" as in the days of sail, and because we are sailing, the direction will only be approximate. You have to obey the wind, and take what shots are offered, but you should be heading generally in the direction your admiral wishes.

I always admonish myself...get in range and fire fire fire. It is the weight of your balls or their rhythm that matter...[Wadmore]

Portugese Iron beat me today, I made a mistake I'd like to share. I blew out his sails using chain shot, and shot away his mizzenmast. Nice shooting . . . except that was all a waste, I never intended to outmaneuver him, I had a 122. So . . the fact is, the two broadsides I used with the chain shot were wasted, I should have stuck with round shot.

When I am in a running battle with another ship, firing broadside after broadside, I will get my basic direction in shape, make sure no one is gonna run into me, then hover above the enemy ship, and direct my fire from there, using my keyboard to steer.

When attacking a bomb go right at it with the odd dodge, but have your cross hairs off to allow the gun crews to figtht fires [Wadmore]

Couple of addendums to Wad's bomb tactic: Remember to lower your sails as or just before you turn, you'll turn faster. if your sails catch fire, immediately drop anchor, as your sails are hauled in the fire is extinguished.

When firing, it is better to take the wait to correct the aim, than only hitting some and then taking the longer wait. Proper aim means right in the middle of whatever you are shooing at. To do that you often have to ignore steamy. Treat him like a mosquito and don't chase him

Chain vs Round shot, at a distance . . a trade off. Using your gun sight set on round shot & broadside, take aim at the enemy. He must be JUST in range of round shot. Then switch to chain shot, whilst still aimmed properly, and fire. You will strip away cannons by the handfull, but barely damage the ship itself.

Wind or Weather Gauge: there are many reasons why being upwind is a tactical advantage. One of them is that when you are upwind, your ship is being pushed so that the side facing the enemy is down (so much so that the lower gun decks would be awash). The enemy, on the other hand, has the same wind pushing on his sails, forcing his hull to be exposed, (showing copper or "heeling"). Each time you exchange broadsides, more of your shot strikes the vulnerable hull. Over time this condition results in an effect known as "having holes in the hull" and leads to sinking :)

Raking is the art of firing into either your opponents bow or stern. These shots are best taken using the "fire at will" button, as we remarked below, the guns will aim centerline. Firing a broadside will waste half your shots, as they travel down the sides of the enemy ship. Likewise . . try to avoid presenting your bow or stern to the enemy, or you will be raked.

If your foe flees, follow. It keeps the pressure on, as well as keeping you near and in charge. Also reduces the amount of time your opponent has to repair.

Wind . . . if you are upwind, you have the "weather gauge", and this is a great advantage, it is you who decides when and if to engage the enemy. And your shot will cary another 25 to 50 yards with the wind . . . fire on the uproll boys.

Wikipedia has very good sections on Naval Artillery, Ships of the Line and Naval Tactics.

Never fire when you have incoming rounds. When you fire you roll the ship, exposing your copper hull. Grit your teeth and take the incoming shots, then fire back. You will have the added advantage of having extra loft given your shot by the rolling of the ship.

A friend, who doesn't like to post, yet peppered me with questions . . " . . there is no range advantage based on the variable of wind . . " My experience is that the physics engine in the game does give a slight wind advantage to the flight of a shot. If you find otherwise, I think the only absolute answer would be from the writers of the algorithms. Which ain't me.

" . . . if you are downwind, many times is an advanage . . . you can disengage faster and get out of trouble" Much truth in this. In fact there was a british admiral who perfected what he called the "Lee side attack" in which the british ships would remorselessly beat to windward, and leaving the enemy no where to run. (You'll have to fill in the blanks on the admirals name, Rodney, I think)

" . . . santismima trinidad has about 20 meters more range than 106 and 122 . . " there is one captain out there who used a Trini to much advantage by pulling just in range and banging away, I would say it is never a good idea to go toe to toe against the Trini. Having said that I have beaten the trini with ships as small as a 74 (not counting the trick of the paddle steamer getting into the Trini's baffles and staying there.