1) Get a core of about 20-40 Line Musket men (I usually get these from Sweden) you can also dismount cavalry units and give them guns if you need more for some reason.
2) Get two groups of mercenary nationalities, equip one of them with swords the other half with pikes etc.
3a) Change the groups of infantry to Swords and Pikes
3b) Change any range cav you're using as musket men to 'Marksmen' if applicable
4) When in battle, put line muskets in front if flat, or near top of hill if not, very tight cluster, 1-2 rows depending on how many muskets, have them fire on your command.
5) Put pike men at the foot of a hill if possible, or just behind the musket men, but off to the left, or right. Very tight cluster, 3 rows. Hold ground.
6) Swordsmen behind pike men, hold ground, very tight clusters, preferably away from firing lines.
7) Wait for people to get in close, start ordering your musket men to fire en mass. This causes horrific injury. As pike men should be very close, if cav survives the volley, send in pike men. Use swords to cut down the rest.