How to use melee cavalry 1- Melee cavalry is a support unit
Melee cavalry cannot win battles by themselves as cavalry will never beat an infantry square and are very vulnerable to musket and artilery fire. This means you shouldn't bring too many cavalry in your army (4 is generally enough), however cavalry when properly used in conjunction with other units will prove a decisive factor in battles. It's important to note that cavalry is least effective in chokepoint maps, so act accordingly.2- Firearms disruption
One of the most useful purposes of cavalry is their ability to impose firearms disruption, meaning they can rob or hamper an opposing infantry's ability to fire their weapons. One way is to force opposing line/elite infantry into a square formation with a real/feint charge, this causes the enemy's total firepower output to be significantly decreased. Second way is to initiate melee with the opposing infantry, as once a unit is in melee most of the unit cannot fire.
Disrupting the enemy's use of firearms opens up many opportunities for your own infantry. Here are a couple example scenarios:
1) You and your opponent's infantry are sitting a short distance outside each other's firing range. You can send in your cavalry at the enemy for firearms disruption, then while your enemy is unable to fire move in your infantry into firing range to get the first volley and subsequent volleys without return fire. Moreover if the enemy infantry got into square formation, then the enemy infantry has presented itself as a ripe musketry target and will increase your infantry's accuracy.
2) You and your opponent's infantry are already in the middle of a firefight. You can then send in your cavalry to hasten the defeat of the opposition, lessen your casualities or turn around a losing engagement.
It is worth noting that cavalry do not last long against infantry in square formation, and your infantry will need to move in fast to take advantage of the situation. Cavalry used to perform firearms disruption should avoid getting shot mid-charge, meaning you should charge from the flanks, rear or while the opposition is reloading. In summary, firearms disruption should be followed up with an infantry push. 3- Chase routing foes.
Routing units have a tendency to come back into battle while units that are "broken" will not. If routing units are attacked while they are fleeing they will be broken, and cavalry's mobility is perfect for the job. Moreover the size of the unit attacking the fleeing unit doesn't really matter, consider using depleted cavalry units for this role. 4- Melee cavalry is very lethal to everything that is not in square formation.
Cavalry are very lethal to units that cannot form a square or even line infantry that where caught out of square. This means cavalry will make short work of artilery and light infantry/riflemen, just make sure to charge from the flanks or rear to avoid getting shot. Cavalry can be used to probe your opponent's attentiveness, especially if you initiate charges on multiple sections of his army simultaneously you could catch your opponent off guard.
Moreover, line infantry already in melee cannot form squares, thus should you use your own infantry to initiate melee you could use the opportunity to charge the backs of the enemy with your cavalry for an old fashioned hammer and anvil. Another important fact is that line infantry at 40 men or below cannot form squares and are very vulnerable to cavalry. 5- Lancers are the best type of melee cavalry
Not only are they cheap, but they will easily chew up even expensive heavy cavalry and absolutely annihilate light cavalry on a good charge. Because lancer's melee stats are usually quite poor, they require a bit of micromanagement as you must pull away your lancers immediately after a charge, and run a distance before re-charging-- in other words cycle charging. 6- Ensure distance between multiple melee cavalry units charging together
Don't blob up your cavalry, not only will they interfer with each other's charge you will also waste manpower and open your cavalry up to be surrounded. 6- Don't buy dragoons with the intention of dismounting
Dismounting dragoons is making an otherwise useful cavalry unit into a useless and overpriced infantry unit. Dismounted dragoons, with so few men, cannot muster much firepower. They can even be beaten by opposing militia whereas mounted dragoons would have. Compounding their problems is that they cannot form square and are extremely vulnerable to other cavalry. Dismounted dragoons do not have much tactical applicability, even for quickly grabbing hills and chokepoints, as they are weak and vulnerable. Keep your dragoons mounted. 7- Don't use the diamond formation
Another improperly coded feature of the game, it decreases the lethality of your cavalry's charge and doesn't confer any bonus manuverability advantages over a regular square-like cavalry formation. In summary, don't use it.
How to counter melee cavalry1- Infantry squares
Infantry squares are basically invulnerable to cavalry. If your opponent is foolish enough to attack with cavalry unsupported, then squares will make short work of them. However, competent players will not charge into already formed squares, thus forming squares at the last minute could trick your opponent into thinking you've been careless.
Moreover, you can lasso enemy cavalry into your squares by getting them to charge your cavalry or light infantry and order your units to run through the square. As the enemy's cavalry chases your unit, your unit will run through the square while your enemy will get caught on the infantry square.
If your opponent is using suported cavalry in a firearms denial fashion, you can respond by counter-charging with your own cavalry and get your infantry out of square formation as soon as possible. Or you can use your cavalry to impose firearms denial to the opponent's supporting infantry to prevent them from shooting at your square.2- Infantry
You can lasso enemy cavalry into range of your light or line infantry to be shot at. Or you can occupy enemy cavalry with your own while you move your infantry into firing range to shoot lethal volleys. Cavalry is very vulnerable to musket fire and moving in ranged infantry support can be very effective if you are outnumbered in the cavalry department.3- Reserve units
Placing a unit of infantry behind another will protect the unit in front from cavalry. If the opposing cavalry charges the unit in front, they will receive a hail of gunfire from the unit in the back. 4- Stakes
Pretty self explanatory, but most competent players will avoid throwing their cavalry upon them. Thus you should use spikes to deny areas, such as beyond your flanks to prevent your opponent from sending calvary around your sides. This potentially forces them to commit to a sucidal frontal charge.
However, you can goad your opponent to run into your spikes. An important fact to know is that your stakes do not hurt your own (or your allies') cavalry thus it is you can order your cavalry to engage the enemy's cavalry and then order your cavalry to run through your spikes while hoping the enemy cavalry pursues.5- Artillery
The large profile of horses makes them ripe targets for all types of artillery. Prioritize the targetting of cavalry.