I think most military wargamers would have no problem with the muskets; btw, you mean tactics not strategy. Best tactics depend on several factors for this game: (1) Composition of enemy forces (2) Composition of your forces (3) Strength Ratio (are you outnumbered, and how badly) and (4) Terrain (and Weather for some mods). For some mods/DLC (e.g. Viking Conquest) you have to factor in fatigue and other factors, which makes it a bit more interesting.
General good practices:
Use the first ten seconds to scan terrain and find the best position to fight from; looking for somewhere that gives you best chance against specific enemy force (see below) and where you can keep weaker forces (shooters) in enfilade and anchor your flanks (use terrain features like trees, buildings, river, cliff to prevent enemy from rolling up your flank). See the solution in your mind and start to reposition forces immediately.
Use terrain masking; this means everyone stays below the crest of hills or is shielded by terrain features so the enemy does not have line of sight (LOS) and thus has no chance to shoot at you (or observe your movement in real world) while you or your forces are moving.
Cavalry is best used for spoiling attacks, breaking lines, rolling up flanks, attacking vulnerable isolated units (musket/archers), and pursuit of retreating army when they break contact.
ENEMY MOSTLY INFANTRY: If you have ranged units, and enemy does not have ranged or cavalry, parking your ranged on a hill with clear line of sight (LOS) in all directions will work fine, with infantry behind for support to close if the enemy makes it that far. If they have ranged also, I would use some terrain masking/ reverse slope, unless you have a real advantage and better ground.
ENEMY MOSTLY CAVALRY: You need to both limit his mobility and anchor your flanks firmly. River banks are great for this, with infantry line in water, shooters just on bank so they catch the cavalry as they crest but aren't so high they catch distant fire. Use banks to anchor flanks. Also steep hills, heavy forest, urban/fences, you get the idea.
ENEMY SUPERIOR RANGED AND NUMBERS: Use reverse slope ambush. Park on reverse slope of hill so they have to come over the top. If they have cavalry, set up a skirmish line of infantry 50 yards down the reverse slope (to allow clearance for your shooters). Put shooters farther down the hill, (or better on small rise beyond base of hill) but KEEP EVERYONE OUT OF LOS of the enemy advance. I use two shooter teams, with one at a flank to place defilade fire into the enemy flank as they crest the hill. If there is a pile of bodies at the top twenty yards of the hill and you take near zero casualties you are doing it right.
I can win most engagements outnumbered very heavily, even against much better forces with virtually no casualties. This is difficulty currently 155%. So many cool battles, recent one was 269 them vs 80 me, them Swedes with Reikers and all high level units, me mostly crap units I was training up but lots of gunners. I used a river/riverbank with nearly perfect force setup and killed nearly every one of the b*stards, and took one killed (infantryman on the skirmish line) and one wounded (Companion). It was a glorious thing!!
The only times I've ever been shot was during the assault while doing the sieges; not much to do there but close in quick as you can, post elite gunners on the walls once inside, and get er done as quickly as possible.
