Focus on it. Not in a literal way, but keep it at the back of your head. It may take weeks or months, but seek and you shall find. DO NOT, seriously, do not, try to bring them to you. Do not put recording devices in your home, or use a Ouija board. It's like a beacon, and if you become sensitive, you will not like the result. Just look for signs, pay attention to the small stuff, and it will slowly become apparent. It may help, as cheesy as this sounds, to go to places where people experience spirits or ghosts. See if you run into anything. Even now, when I hear something out loud, it freaks me right the fuck out. I know damn well I am impervious, but I still freak out. It's instinct. You'll see, trust me
Don't forget this: KNOW what you are experiencing is real. You will question your sanity at times, but when you have others with you and they experience it too, you will have the validation you need to determine the reality of the situation.