To me a "maniac" is someone, who play to many
hands, and they also tend to play them in an aggressive way. So basically just think about, how you want to adjust against someone, who can have a wider than normal range, and who is perhaps also more likely to bet or raise than other players? Some of the reasonable adjustments, that come to my mind, would be:
*
bluff less which will also include opening less marginal hands preflop, if the maniac is still left to act, and especially if he has position on you.
* Fold less to bets and raises. Maybe AJ is normally a fold to a 3-bet, if you opened from early position, but not against a maniac.
* Value bet thinner. Since the maniac can have a wide range, he have more junky hands, he might call you with, especially because this kind of player typically dont want to give up.
* Take check-to-induce lines more often especially if you are out of position.
In general with maniacs the way to beat them is to let them win many small pots, but then you win most of the big pots, when you have a hand. In cash games you also want to not have these players on your direct left, because that is going to make the session a pure hell. If you find a maniac on your direct left, table change or seat change is a completely legit option. In tournaments you obviously can not do that, but in MTTs you can hope for one of you to get moved to another table, or that the maniac lose his chips.