Proactive interference causes problems with newly acquired information because of older information causing interference or confusion. So, for example, when asked for your current, new address, remembering only your recent, old address. Or, calling your new significant other by someone else's name from the past! Retroactive interference occurs when you learn something new, and it makes it harder to remember the older information that is related. This happens, for example, when you apply for a job and have to try to remember your three last addresses for a background check.
Personal story - when I brought home my new puppy last week, I kept slipping into calling him by my last dog's name. Hence - proactive interference!
When I teach this, I tell my students to keep them straight by simply thinking of the direction the interfering (more easily remembered) information goes - when it goes forward, it is proactive, when it goes backward, it is retroactive.