In marriage, I think a big pitfall is not working on it. That is, not working at making time to be together and bond as a couple.

Also, attempting to mind-read instead of just waiting to hear or asking and seeing what he/she says is up.

Nagging is not a successful tactic. Nor is anger. Nor is constant criticism.

Dishonesty

Completely ignoring a partner's likes/dislikes and/or strong feelings about something and doing it anyway is never a good thing.