I am by no means a veteran map maker but just as a general rule of thumb I try to do for one team the same that I do for the other. Not the exact same artifacts and treasures for each side, but the same amount of artifacts from each category. If you're doing a specific type of town then I would place powerups that are going to be beneficial to the respective types of towns.
as far as landscape goes I like to make a bit more challenging to get to the opponent's town. placing mountains and other obstacles in a way that will take the hero on a bit of a journey.
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