My most succesful tactic to date has been finding sharp, pointy, Russian things, and pushing them into soft Polish people. Worked a treat.

boyar-Sons were the real deciding factor - I found Alexandrian tactics worked well - create a spear-line, with archery backup, and calvalry on the wings, slightly back from the front line.

March into archery range.
Wait for the Poles to engage your spears.
Hit them in the flank & rear with calvalry.

One key tip - when charging their calvalry, if you have 2 calvalry units on the wing (which you probably do), tell the nearest to charge directly. Tell the 'outside' unit to march move behind the enemy. Wait for them to form up, then charge. Much more effective than sending 2 calvalry units into the flank.

Only difficulty I had was with Polish Nobs, and they were never deployed in sufficient force or intelligence to cause any real problems.