Celtic rituals I've studied in the past include:

Carrying burning sage around the perimeter of the home. This is to cleans the area around the home so no ill may pass.

With a new broom (preferably one you made yourself, or you can get a straw broom and tuck the herbs inside the bristles) that contains rue and heather. Sweep the house from the back door to front, shake the broom outside and carry it back in. This broom will bring happiness to the home and cast out any spirits that may have tried to enter before you moved in.

Rue is always a good choice for bringing into a new home. Note that Rue brings the most luck to you if you steal it. (I just usually tell a friend that some of her rue will mysteriously vanish)

Bloodroot draws love and avert negativity; place on doorways and windows for protection

Planting male and female holly around the house is another way to bring blessings onto the dwelling, especially if you are wanting to have children.

Anise wards off evil and is best planted in a circle.