I’ll start by saying that I don’t claim to know what “ghosts” are or what you mean by the term. I’ll go on to say that I have done several house blessings/cleansings and assisted with one exorcism.
House cleansings are very easy, and you can do it yourself. In my religion, we start with cleansing ourselves, either with a spirtually minded bath or sage smoke (or both.) Then we start on the house with a broom. Sweeping everything very thoroughly, use whatever chant or song or mantra you like to reinforce spiritual cleanliness. I like “This home is safe, this home is clear; negative energy, get outta here!” Some people like the Lord’s Prayer. You can google “house cleansing chants” for ideas and see what resonates with you. Keep sweeping and repeating your chant, and this will get you into a nice light trance space for the next step.
Using sage (bundles are nice for this) or incense or salt or water or scented oil, move to each window and doorway. You can let the smoke waft or sprinkle the salt, water or oil, or you can make a symbol with it that feels protective to you. I use pentacles myself, some people use the sign of the cross, others a spiral. Again, what feels right to you is more important than what the books say. As you do this, imagine a bright white light emanating from your tool and spreading over the window/door. As you progress through the house, feel that light spreading until your entire home is covered with it.
If you find an area of resistance (which might feel literal, like you can’t move your tool, or it might feel like boredom or fatigue), you’ve found a spot which may need a little more effort. Usually repetition does the trick. If it doesn’t, make note of the spot; you may need to call in someone with more experience to help you there.
When you’re done, finish with another mantra, prayer or chant. “Light space, white space, mine to fill with love and joy, so mote it be.” Or the Lord’s Prayer. Or google again for more options.
I’ve done these types of house cleansings for neopagans, for Christians, for atheists and more. It doesn’t seem to matter what people believe or don’t, the ritual actions make them feel better and more in ownership of their space.
If you believe you have a specific entity causing trouble, you can do much the same, focusing on the area where you most feel its presence. Follow Dr. Drake’s steps above. Call it, find out what it wants, see if you can accommodate it. If you can, do so. If you can’t, tell it so. Most of the time it will go away if you communicate honestly the reason you can’t help it. Ghosts (whatever they are) are generally not really focused on scaring people, they’re trying to get assistance. If you can make it believe you can’t help it, it will look for someone who can and leave you alone.
I’m an agnostic neopagan myself. I don’t know what’s true, I just use what works for me and those who request my services.