I find that a good tactic is to pair up your melee infantry and line infantry (if you happen to be a faction that has both). For instance, Russia.
Russian cossacks are balls at melee, but the streltsy are pretty good at it. Hence, you line your streltsy up behind the cossacks, and, when it comes time for the charge, have your streltsy run THROUGH the Cossacks.
Not only do you get the melee bonus, but you preserve your melee unit and let them fight against a much weaker enemy.
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